Nowadays there seems to be an app for everything. And mobile apps have been a part of our life. The following apps are part of the most popular apps.

    We know the mosquito very well. Mosquitoes fly everywhere. They can be found almost all over the world, and there are more than 2,500 kinds of them.

    No one likes the mosquito. But the mosquito may decide that she loves you. She? Yes, she. It's true that male mosquito doesn't bite(咬) and only the female mosquito bites because she needs blood to lay eggs. She is always looking for things or people she wants to bite. If she likes what she finds, she bites. But if she doesn't like your blood, she will turn to someone else for more delicious blood. Next time a mosquito bites you, just remember you are chosen. You're different from the others!

    If the mosquito likes you, she lands on your body without letting you know. She bites you so quickly and quietly that you may not feel anything different. After she bites, you will have an itch(痒) on your body because she puts something from her mouth together with your blood. By the time the itching begins, and she has flown away.

    And then what happens? Well, after her delicious dinner, the mosquito feels tired. She just wants to find a place to have a good rest. There, on a leaf or a wall, she begins to lay eggs, hundreds of eggs.

    Oh, the places you'll go!

    When it comes to habitat, human beings are creatures of habit. It has been known for a long time that, whether his habitat is a village, a city or, for real globe-trotters (周游世界者), the planet itself, an individual person generally visits the same places regularly. The details, though, have been surprisingly obscure. Now, thanks to an analysis of data collected from 40,000 smartphone users around the world, a new property of humanity's locomotive (移动的) habits has been revealed.

    It turns out that someone's "location capacity", the number of places which he or she visits regularly, remains constant over periods of months and years. What constitutes a "place" depends on what distance between two places makes them separate. But analyzing movement patterns helps illuminate the distinction and the researchers found that the average location capacity was 25. If a new location does make its way into the set of places an individual tends to visit, an old one drops out in response. People do not, in other words, gather places like collector cards. Rather, they cycle through them. Their geographical behavior is limited and predictable, not fancy-free.

    The study demonstrating this, just published in Nature Human Behavior, does not offer any explanation for the limited location capacity it measures. But a statistical analysis carried out by the authors shows that it cannot be explained solely by constraints on time. Some other factor is at work. One of the researchers draws an analogy. He suggests that people's cognitive capacity limits the number of places they can visit routinely, just as it limits the number of other people an individual can routinely socialize with. That socialization figure, about 150 for most people, is known as the Dunbar number, after its discoverer, Robin Dunbar.

    Lehmann says his group is now in search of similar data from other primates (灵长目动物), in an attempt to work out where human patterns of mobility have their roots. For those, though, they will have to rely on old-fashioned methods of zoological observation unless they can work out a way to get chimpanzees to carry smartphones.

    What makes a gift special？Is it the price you see on the gift receipt？Or is it the look on the recipient's face when they receive it that determines the true value? What gift is worth the most?

    This Christmas I was debating what to give my father. My dad is a hard person to buy for because he never wants anything. I pulled out my phone to read a text message from my mom saying that we were leaving for Christmas shopping for him when I came across a message on my phone that I had locked. The message was from my father. My eyes fell on a photo of a flower taken in Wyoming, and underneath a poem by William Blake. The flower, a lone dandelion standing against the bright blue sky, inspired me. My dad had been reciting those words to me since I was a kid. That may even be the reason why I love writing. I decided that those words would be my gift to my father.

    I called back. I told my mom to go without me and that I already created my gift. I sent the photo of the cream-colored flower to my computer and typed the poem on top of it. As I was arranging the details another poem came to mind. The poem was written by Edgar Allan Poe； my dad recited it as much as he did the other. I typed that out as well and searched online for a background to the words of it. The poem was focused around dreaming, and after searching I found the perfect picture. The image was painted with blues and greens and purples, twisting together to create the theme and wonder of a dream. As I watched both poems passing through the printer, the white paper coloring with words that shaped my childhood. I felt that this was a gift that my father would truly appreciate.

    Christmas soon arrived. The minute I saw the look on my dad's face as he unwrapped those swirling black letters carefully placed in a cheap frame, I knew I had given the perfect gift.

    I remember meeting him one evening with his pushcart. I had managed to sell all my papers and was coming home in the snow. It was that strange hour in downtown New York when the workers were pouring homeward in the twilight. I marched among thousands of tired men and women whom the factory whistles had unyoked. They flowed in rivers through the clothing factory districts, then down along the avenues to the East Side.

    I met my father near Cooper Union. I recognized him, a hunched, frozen figure in an old overcoat standing by a banana cart. He looked so lonely, the tears came to my eyes. Then he saw me, and his face lit with his sad, beautiful smile-Charlie Chaplin's smile.

    "Arch, it's Mikey," he said. "So you have sold your papers! Come and eat a banana."

    He offered me one. I refused it. I felt it crucial that my father sell his bananas, not give them away. He thought I was shy, and coaxed and joked with me, and made me eat the banana. It smelled of wet straw and snow.

    "You haven't sold many bananas today, pop, "I said anxiously.

    He shrugged his shoulders.

    "What can I do No one seems to want them."

    It was true. The work crowds pushed home morosely（愁眉苦脸的）over the pavements. The rusty sky darkened over New York buildings, the tall street lamps were lit, innumerable trucks, street cars and elevated trains clattered by. Nobody and nothing in the great city stopped for my father's bananas.

    "I ought to yell," said my father dolefully. "I ought to make a big noise like other peddlers, but it makes my throat sore. Anyway, I'm ashamed of yelling, it makes me feel like a fool. "

    I had eaten one of his bananas. My sick conscience told me that I ought to pay for it somehow. I must remain here and help my father.

    "I'll yell for you, pop," I volunteered.

    "Arch, no," he said," go home; you have worked enough today. Just tell momma I'll be late. "

    But I yelled and yelled. My father, standing by, spoke occasional words of praise, and said I was a wonderful yeller. Nobody else paid attention. The workers drifted past us wearily, endlessly; a defeated army wrapped in dreams of home. Elevated trains crashed; the Cooper Union clock burned above us; the sky grew black, the wind poured, the slush burned through our shoes. There were thousands of strange, silent figures pouring over the sidewalks in snow. None of them stopped to buy bananas. I yelled and yelled, nobody listened.

    My father tried to stop me at last." Nu," he said smiling to console me," that was wonderful yelling, Mikey. But it's plain we are unlucky today! Let's go home."

    I was frantic, and almost in tears. I insisted on keeping up my desperate yells. But at last my father persuaded me to leave with him.

    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 went to Harvard. An approving eye glinted 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, wasting 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.