1 . Who is to blame for the shapes of our noses?

If you are not satisfied with the shape of your nose, blame it on climate, not your parents or grandparents. In a study published this week in the journal PLOS Genetics, researchers from the Pennsylvania State University found that human noses may have been shaped, in part, by a long process of adaptation to local climate conditions.     1    .

The findings were based on an examination of the size and shape of noses on people with West African, South Asian, East Asian, or Northern European ancestry. It showed that the width of the nostrils is strongly related to temperature and absolute humidity (绝对湿度), but not the result of genetic drift (遗传漂变).

One purpose of the nose is to condition the air we breathe, to ensure that it is warm and moist when it reaches the lungs, which helps to prevent infections.     2    which was probably more essential to have this trait in cold and dry climates, it said.

People with narrower nostrils probably had better and had more offspring than people with wider nostrils, in colder climates.    3    . The nose has had a complex evolutionary history, however, and researchers suspected that additional factors, such as cultural preferences when picking a mate, have also pl played a role in shaping the nose.     4    . Studies of human adaptation are essential to our understanding of disease and yield insights into why certain conditions, such as skin cancer, are more common in certain populations.

The researchers said that it may be worth investigating whether the shape of the nose impacts ones risk of contracting breathing diseases when living in a climate that is different from one's ancestors.

Not everyone is born with beautiful hair, but by learning a few hair care facts, you can make your hair look its best. Healthy, attractive hair should     1    . Whether your hair is long or short, light or dark, it should look smooth, silky and     2    . Everyday events such as shampooing, brushing and blow     3     can do great damage to your hair, causing the dry, brittle and frizzy appearance.

When you     4     your hair, you should use a shampoo for your specific type of hair. If you have permed [烫(发)] or color treated hair, you should use a shampoo for chemically treated hair. Many people believe that baby shampoo is very gentle and safe to use on their hair. This is a wrong idea. Leave the baby shampoo for your baby. If you are not sure what your hair type is or what type of shampoo to use, ask your     5    . Your hairdresser can recommend a specific shampoo and     6     to keep your hair healthy and shiny.

Brushing your hair can actually help improve the shine. You should never brush wet hair. When hair is wet it is much weaker than when it is dry. Wet hair will break very easily if it is not combed very gently. Never     7     your hair between the towel to dry it, for this can cause severe breakage. Before combing, a leave-in conditioner should be sprayed on the hair to help restore shine and help remove tangles. Using a wide tooth comb,     8     hair from the ends and work your way up.

Blow     9     are very convenient and many of us use them daily. If they are used incorrectly, they can cause severe heat damage to your hair. You should allow your hair to air dry until it is about half way dry. If you follow these healthy hair practices, you should notice an improvement in the condition of your hair within two to four weeks, depending on how       10     your hair is.

4 . It seems that everyone seeks for bright white teeth. There are whitening materials in toothpastes, mouthwash, and even chewing gum. Yellow teeth seem to get a bad reputation and are usually associated with poor oral hygiene (卫生) . Fortunately, we have some good news for those who lack those pearly whites. Yellow teeth are actually stronger than bright white teeth!

We know, it's hard to believe. According to sciencefocus. com, the enamel (珐琅质) on your teeth is naturally a blueish white color and the dentine ( 牙质) beneath it is naturally yellow. Since the enamel is semitransparent, the yellow shows through the blueish white. This creates a light grey or light yellow color. However, if your teeth are significantly darker than a light yellow， there may be a potential cause such as disease or tooth decay.

The process of bleaching your teeth is what weakens them.“Some products contain hydrogen peroxide (过氧化氢) that spread through the enamel. It breaks down the compounds that are causing color changing, and your teeth become lighter, ”Adriana Manso, a clinical assistant professor in the Faculty of Dentistry, told The University of British Columbia.

“Those products can have multiple side effects such as damaging the dental enamel, causing harm to the gums, tooth sensitivity and more,” Manso adds.“Some of these effects are lasting; for example, the damage to the dental enamel is permanent and irreversible.

If you sill long for those white teeth though, there are plenty of chemical-free routes to take that won't damage your enamel一like eating celery, spinach, onions, carrots, shiitake mushrooms, peanuts or drinking green tea, or consulting a doctor to try, other more advisable ways to naturally brighten your teeth.

6 . Who doesn’t dream of a bright, beautiful, pearly-white smile? It’s something most of us long for — after all, great teeth are a sign of good health, fortune, and youth.     1    . It's people's lifestyles that are contributing to poor tooth health. Here we have listed the worst habits for your teeth.

Avoiding your dentist (牙医)

How often do you go to the dentist?     2     According to reports, around 33 percent of the population in Britain do not visit their dentists as often as they should. This is unfortunate as seeing a dentist regularly is often your first line of defence against more severe dental diseases.

    3    

For some reason, most people get into the habit of moving their brushes back and forth over their teeth. Now, you may think that this is getting rid of all the germs (细菌) but there are actually better methods you should employ. Instead of back and forth, you should be using short, circular movements to brush your teeth.

Not flossing (用牙线清洁牙齿) regularly

    4     However, this simply isn’t the case. Though regular brushing gets rid of the germs on the surface of your teeth, it often has little impact on the food stuck between your teeth, which is all germs need. This is why it is important to floss at least once a day.

Sipping sugary drinks all day

By drinking sugary drinks throughout the day, your teeth are being exposed to sugar for greater amounts of time which can lead to higher levels of tooth decay (蛀蚀) and other oral health issues. So, what should you do? Well, to start with, try to reduce your intake of sugary drinks as much as possible.     5