Nowadays people’s screen time is really much. Both adults     1     teens spend a large deal of time in front of their smart phones, computers and TVs. It     2    (show) that nearly one-third of adults spend more than half their awake time     3    (use) smart phones, iPads or computers. As for teens, they spend over seven hours every day in front of screens.

Looking at a screen for a long time is harmful     4     our eyes. Our eyes hurt if they get     5    (tire). Our eyesight may become even     6    (bad) in the long term. Doctors suggest that we take     7     break from screens every 10 to 20 minutes. Whenever our eyes hurt, even if they hurt slightly, we should immediately take a step back from the screen     8    (relax) our eyes.

In today’s society, it may not seem that we can cut screens out     9    (entire). But with     10    (disadvantage) that can affect our eyes, there is a good reason to cut down our screen time.

5 . Wisdom teeth seem like a biological mistake, leading to millions of surgeries per year. But for some people, these “extra” teeth come up just fine, while others don’t get them at all. What’s the biological story here?

According to the standard story, before surgical intervention, people with impacted wisdom teeth expired. Those lacking the problematic teeth increased in number, passing on genes for reduced numbers of teeth to future generations. Today, thanks to dental surgeons, individuals with impacted teeth survive and contribute to the gene pool.

But decades of research challenges this survival-of-the-toothless explanation. Many scholars now propose that wisdom teeth problems originate from our eating softer foods as children, made possible by farming and industrialization. Here’s the theory: Compared to wild resources consumed by hunter-gatherers, agricultural and processed foods are softer. Hard food during childhood seems to stimulate jaw growth, allowing mouths to grow large enough for more teeth. Soft food doesn’t require enough of a chewing workout to maximize jaw growth potential.

Around 12,000 years ago, humans began to experiment with farming, and this lifestyle ultimately took hold in most societies. Domesticated products, like wheat flour and cow’s milk, make for much softer diets than wild foods. What’s more, the industrialization of food production has really softened our meals. So the idea is that processed and/or agricultural diets reduce the stress on our jaws necessary to result in full growth when we reach early adulthood. By the time we’re reaching adulthood, there may not be enough space to accommodate our final molars (臼齿).

This theory is supported by research. For example, a 201l paper measured skulls housed in museums from six farming and five hunter-gatherer groups. The farmers, raised on softer foods, consistently had shorter jaws, which would have provided less space for tooth formation.

Consequently, many dental scientists recommend parents put some additional raw fruits, vegetables and nuts on kids’ plates, which could potentially prevent later wisdom teeth removals.

6 . Scientists recently discovered that our brains may be just as busy at night as they are during the day. While we sleep, our brains are doing much more than getting ready for the next day. Scientists found that the brain may be busy cleaning out harmful waste materials.

As with many studies, scientists turned to mice for help. They studied the mice brains as they slept and when they were awake. They saw that the brains of sleeping mice were hard at work.

Dr. Maiken led the study. The brain expert says our brains perform two very different jobs. It seems they have daytime jobs. Later they “moonlight” at a nighttime job. And this study says that is what our brains seem to be doing. “When we are awake, the brain cells are working very hard at processing all the information around us. When we are asleep, they work very, very hard at removing all the waste that builds up when we are awake.” The scientists say that the waste material includes poisons.

They also found that during sleep, the brain’s cells become smaller, which allows waste to be removed more successfully. Dr. Maiken says these poisons end up in the liver(肝脏). There, they are broken down and then removed from the body. “So we need to sleep because we have a cleaning system that removes many of the poisonous waste products from the brain.”

Dr. Maiken says the next step is to look for the process in human brains. She says the results show how important sleep is to health and fighting disease. The research may also one day lead to treatments to prevent or help fight mental disorders(精神疾病).

9 . Back pain can make it difficult for many people to function in everyday life.     1     If you suffer from back pain, read on for four everyday fixes.

Our bodies need adequate movement throughout the day to avoid the stiffness that contributes to aches and pains. If the weather is good, don't hunt for the nearest parking spot; don't take the elevator when you have the option of one or two flights of stairs. When you need to sit for long periods, set a timer to get up every hour and be active for just a few minutes.     2    

When we overuse our dominant side, we create muscle patterns of weakness and tension that increase pain, especially in our backs. Consider the actions you take repeatedly throughout the day that shift your weight to one side.     3     And use your opposite hand every so often for basic activities, such as opening doors.

Psychological stress is a noted risk factor for back pain, according to research. Most mental stress is caused by focusing on the past or future.     4     A few minutes a day of mindfulness can go a long way toward minimizing the impact of stress. Additionally, mindfulness practices like tai chi have all shown effectiveness in reducing back pain.

    5     That is, you can create a game plan of daily activities to practice for back health. If your back hurts at the end of the day, don't just decide it was a “bad” day. Ask yourself if you practiced the activities to help you avoid the stress and tension. Taking an active, daily-life approach to maintaining a healthy body is the key to keeping back pain at bay.