1 . Perhaps you use your headphones to enjoy music and peace and quiet during the day. But you may be neglecting the dangers of hearing loss with headphones.
In fact, headphones are not a bad thing. They can bring peace, allow for better musical enjoyment, and even protect your ears from higher decibels(分贝).
How long should you wear your headphones every day? The answer is, according to the World Health Organization, one hour per day.
Then, how do you set the safest volume for your headphones? With headphones, it depends on the type you’re using and your environment. To test things out, you should take them off your ears and extend them in your hands out in front of you.
| A．This might seem unreasonable to you. |
| B．At times, hearing loss isn’t permanent. |
| C．l in 5 teens will have some types of hearing loss. |
| D．What’s more concerning is what that means for children. |
| E．It’s the duration and volume that cause the problem, however. |
| F．If you still hear your music clearly, you need to turn them down. |
| G．It’s a wonderful thing to shut out the rest of the world and enjoy your music. |
1. How long is that since the woman’s last visit here?
| A．Over a year. | B．Over half a year. | C．Over a couple of months. |
| A．She has a toothache. |
| B．She lost a tooth. |
| C．She feels uncomfortable when eating something cold. |
| A．Go away. | B．Get her teeth fixed. | C．Get her teeth further examined. |
3 . Most of us learned what we know about eye color from a chart in grade-school biology. You know two blue-eyed parents are going to have blue-eyed kids. But the story of how eye color is passed down is more complicated（复杂的) than we’re taught.
Humans get their eye color from melanin（黑色素）, which also determines skin and hair shades. Melanin is good at absorbing light, which is especially important for the iris（虹膜）, the function of which is to control how much brightness can enter the eyes. Once it passes through the irises, the majority of the visible light goes to the retina（视网膜）, where it’s translated into images by the brain. The little that isn’t absorbed by the iris is reflected back, producing what we see as eye color. That color depends on the kind and amount of melanin a person is born with.
Though we used to think eye color just came from a simple pattern of inheritance （遗传）, in recent years scientists have found that it’s also shaped by many genes acting together. What’s more, tiny changes, or mutations（突变）, in a gene can result in different shades in the iris.
The two genes currently thought to be most strongly linked with human eye color are OCA2 and HERC2. OCA2, the gene we used to think was the only player in eye color, controls the production of the P-protein and the organelles that make and transport melanin. Different mutations in the OCA2 gene increase or decrease the amount of protein that’s produced in the body, changing how much melanin is sent to the irises. The HERC2 gene, meanwhile, acts like a helicopter parent （直升机父母） for OCA2. Different mutations in this gene act as a switch that turns OCA2 on and off and determines how much P-protein it produces.
Those are just the two genes we know about in detail so far. Newer studies have linked as many as 16 genes to eye color, all of which pair with OCA2 and HERC2 to generate different iris colors and patterns. With all these genes and their structural changes, it’s hard to say for sure what a child’s eye color will be based on their parents’.
1. Which of the following shows how light reaches the brain?| A．The irises→ melanin→ the brain. |
| B．The retina→ melanin→ the brain. |
| C．The irises→ the retina→ the brain. |
| D．The retina- the irises -the brain. |
| A．OCA2 is controlled by HERC2. |
| B．OCA2 can be changed into HERC2 |
| C．Both can make and transport melanin |
| D．Both are the cause of mutations in genes. |
| A．Different colors received by the retina. |
| B．A lot of genes as well as their mutations |
| C．The amount of protein the person has in his or her body. |
| D．OCA2 and how much melanin it produces and transports. |
| A．Whether the melanin plays a key role in mutations. |
| B．Whether oCA2 and HERC2 can influence each other. |
| C．Whether melanin results in different shades in the iris. |
| D．Whether your eye color just comes from your parents. |
4 . Losing a baby tooth can be fun for a kid. You can put it under your pillow and look forward to finding some money there in the morning. And then you can watch your new permanent(永恒的）tooth grow in its place.
But if a permanent tooth falls out, that's a problem. There isn't another one under the gum（齿龈）that can replace it. Unfortunately, this happens to some older people. And if permanent teeth fall out or need to be pulled, an older person might need dentures.
Dentures,known as false teeth, are a set of replacement teeth for any teeth that are missing.
There are partial dentures, which take the place of only a few teeth and prevent the others from changing position. If all the teeth are gone, the person would need complete dentures,which replace every tooth in the mouth.
Dentures can cause pains at first but take little time to get used to.They also need special care. They should be brushed daily with a special denture brush and cleanser and soaked(浸泡） in denture solution when not in the mouth.
Dentures are important for the old because, without teeth, it's hard to smile, talk, and eat properly. But it can be a little weird if you see someone take out his or her dentures. It can also be strange to see someone, like a grandparent, without dentures in because he or she won't have any teeth. Try not to make fun of the person because this could cause hurt feelings.
People usually lose their permanent teeth due to periodontal disease (牙周炎）， or gum disease, which is caused by bacteria that attack the gums. Diseased gums aren't strong and healthy, so teeth can get loose and fall out. Older people often have many cavities (洞） that have been filled over the years, and these fillings can weaken over time, leading to more tooth problems.
1. If one of your baby teeth falls out, you_______| A．should have a false tooth fixed in its place |
| B．will gain a permanent tooth in future. |
| C．have to put it under your pillow at once |
| D．can exchange it for some money |
| A．will experience unpleasant feelings at the beginning |
| B．will spend a very long time adjusting himself or herself to them |
| C．should brush them with a special denture brush every few days |
| D．should use denture solution to soak them in his or her mouth |
| A．Partial dentures can prevent the remaining teeth from changing position. |
| B．Old people will find it hard to smile, talk, and eat properly without teeth. |
| C．A person's teeth will possibly get loose if diseases strike his gums. |
| D．It is hard for a person to wear dentures if all his teeth have fallen out. |
| A．inconvenient | B．excited | C．strange | D．impolite |
