Many young students consider their friends as the most important people in their lives. They believe that their family members, especially their parents, don't know them as well as their friends do. In large families, it is often for brothers and sisters to fight with each other and then they can only go to their friends for advice. It is very important for young students to have one good friend or many friends. Even when they are not with their friends, they usually spend a lot of time talking among themselves on the phone. This communication is very important in children's growing up, because friends can discuss something difficult to say to their family members.

    However, parents often try to choose friends for their children. Some parents may even stop their children from meeting their good friends. The question of “choice” is an interesting one.

    Have you ever thought of the following questions?

    Who chooses your friends?

    Do you choose your friends or your friends choose you?

    Have you got a good friend your parents don't like?

    Dr. Sasaki knew the first-night effect probably has something to do with how humans evolved.

    The puzzle was what benefit would be gained from it when performance might be affected the following day. She also knew from previous work conducted on birds and dolphins that these animals put half of their brains to sleep at a time so that they can rest while remaining alert enough to avoid predators (捕食者). This led her to wonder if people might be doing the same thing. To take a closer look, her team studied 35 healthy people as they slept in the unfamiliar environment of the university's Department of Psychological Sciences. The participants each slept in the department for two nights and were carefully monitored with techniques that looked at the activity of their brains. Dr. Sasaki found, as expected, the participants slept less well on their first night than they did on their second, taking more than twice as long to fall asleep and sleeping less overall. During deep sleep, the participants' brains behaved in a similar manner seen in birds and dolphins. On the first night only, the left hemispheres (半球) of their brains did not sleep nearly as deeply as their right hemispheres did.

    Curious if the left hemispheres were indeed remaining awake to process information detected in the surrounding environment, Dr. Sasaki re-ran the experiment while presenting the sleeping participants with a mix of regularly timed beeps (蜂鸣声) of the same tone and irregular beeps of a different tone during the night. She worked out that, if the left hemisphere was staying alert to keep guard in a strange environment, then it would react to the irregular beeps by stirring people from sleep and would ignore the regularly timed ones. This is precisely what she found.

    First it was worry about second-hand smoke, now there's major concern over third-hand smoke which gets into hair, clothes, furniture or a car rather than directly from a cigarette or someone breathing it out.

    To be honest, I've always been worried about the health dangers of this even though I didn't know it had a name. My worry made me reluctant to let smokers hold my babies even though they didn't smoke in my house.

    Tests for its effects have been only carried out on mice, but I don't think they can be ignored. Researchers at California University last month suggested third-hand smoke (THS) could cause type 2 diabetes, liver and lung damage.

    They analyzed how people are affected by taking in smoke from another person's clothing, hair, home, or car. They say they can see an impact on the brain and liver. Lead author Manuela Martins-Green said: “Our goal was to decide the smallest amount of time required to cause physiological changes in mice when they are exposed(暴露) to THS.” This was done using an exposure system that is the same as human exposure.

    “We found THS exposure as early as one month caused liver damage. Exposure for two months lead to further molecular(分子的) damage, and at four to six months caused even more such damage. We also found the mice showed insulin resistance（抗胰岛素） after long-term exposure.”

    “THS is a hidden danger, a silent killer. Pollutants can be absorbed through the skin and through breathing.”

    “Although our research was not done on humans, people should be aware that hotel rooms, cars and homes that were used by smokers are very likely to be polluted with THS.” Martins-Green believes most people don't know they're being exposed to THS, or don't believe in the damage it can do.

    THS toxins(毒素) remain on surfaces for many years, and resist even strong cleaning agents.

    A few weeks ago, I called an Uber to take me to the Boston airport for a flight home for the holidays. As I slid into the back seat of the car, the warm intonations（语调）of the driver's accent washed over me in a familiar way.

    I learned that he was a recent West African immigrant with a few young children, working hard to provide for his family. I could relate: I am the daughter of two Ethiopian immigrants who made their share of sacrifices to ensure my success. I told him I was on a college break and headed home to visit my parents. That's how he found out I go to Harvard. An approving eye glinted（闪烁）at me in the rearview window, and quickly, we crossed the boundaries of rider and driver. I became his daughter, all grown up – the product of his sacrifice.

And then came the fateful question: "What do you study?" I answered "history and literature" and the pride in his voice faded, as I knew it might. I didn't even get to add "and African-American studies" before he cut in, his voice thick with disappointment. "All that work to get into Harvard, and you study history?"

    Here I was, his daughter, squandering the biggest opportunity of her life. He went on to deliver the age-old lecture that all immigrant kids know. We are to become doctors (or lawyers, if our parents are being generous) – to make money and send money back home. The unspoken demand, made across generations, which my Uber driver laid out plainly, is simple: Fulfill your role in the narrative（故事）of upward mobility so your children can do the same.

I used to feel anxious and backed into a corner by the questioning, but now as a junior in college, I'm grateful for their support more than anything. This holiday season, I've promised myself I won't get annoyed at their inquiries. I won't defensively respond with "but I plan to go to law school!" when I get unrequested advice. I'll just smile and nod, and enjoy the warmth of the occasion.

    My mother loves flowers. As soon as warm weather comes around, you will find her planting, watering and weeding over everything. For many years we lived next door to each other, and she spent as much time in my garden as she did her own. After the flowers became plentiful each summer, she would cut colorful bouquets (花束) to enjoy inside the house－both hers and mine. I would often come home from work and find a beautiful arrangement (布置) of fresh flowers on my coffee table.

    Shortly before Christmas one year, a local flower shop offered a bouquet month special. It seemed to be a great way to thank her for all of the flowers she had given me through the years. After the holidays, in early January, I drove her to the flower shop to pick up her first month's bouquet. The small fresh colorful bouquet would hardly fill a small vase (花瓶).

    I was so embarrassed(尴尬的). However, after we returned home, she began to arrange the flowers she had received. “Mom, I'm sorry,” I told her. “I can't believe how skimpy that bouquet is.” She looked at me and smiled. “It's okay,” she said. “It allows me to better enjoy the beauty of each one.”

    Mom's words helped me to realize something bigger and more important－when we have too many good things, we often fail to enjoy the beauty of each one.

      Thanks, Mom, for helping me understand that less is sometimes more.

    While elephants born without tusks (长牙)are not unheard of，they normally form just 2 to 6 percent of the population. However, that is not the case at Mozambique's Gorongosa National Park, where an astonishing 33 percent of female elephants born after the country's civil war ended in 1992 are tuskless. While that may appear to be just a coincidence, Joyce Poole, an elephant behavior expert, has another theory. The researcher thinks we may be witnessing unnatural evolution of the species due to the constant hunting of elephants for valuable ivory.

    Poole says before the country's 15-year-long civil war, the 100,000—acre park was home to over 4,000 elephants. However, by the time the conflict ended in 1992, about 90 percent of them had been killed for ivory to help finance weapons (武器)and meat to feed the soldiers. Of the less than 200 survivors, over 50 percent of adult females had no tusks. Therefore, it is not surprising that the park's tuskless elephant population has grown greatly.

    This is not the first time researchers have observed a great change in the population of elephants. At Zambia's South Luangwa National Park and Lupande Game Management Area ， areas which were heavily hunted in the 1970s and 1980s, 35% of elephants 25 years or older and 13% of those younger than 25 are now without tusks. A 2008 study published in the African Journal of Ecology found that the numter of tuskless females at the Ruaha National Park in Tanzania went from 10.5 percent in 1969 to almost 40 percent in 1989, largely due to illegal hunting for ivory.

    The recent ban on ivory in both the US and China should help get rid of, or at least reduce, elephant hunting. However, scientists are not sure how long it will take for elephants with a higher rate of tuskless females, to change the trend.