As we know, the world has a population of 6.8 {#blank#}1{#/blank#} (billion/billions) and it is increasing {#blank#}2{#/blank#} (by/to) 80 million every year. China has already {#blank#}3{#/blank#} (reach/reached) 1.3 billion, so it has the largest population in the world. It's reported that the population in developing countries {#blank#}4{#/blank#} (is/are) larger and is growing faster than {#blank#}5{#/blank#} (those/that) in developed countries.

As a result, the population problem has become more serious in {#blank#}6{#/blank#} (developing/developed) countries. 

    Who designed (设计) the first helicopter (直升机)? Who{#blank#}1{#/blank#} one of the most famous pictures in the world? Who knew more about the human body than most {#blank#}2{#/blank#}? There is an answer to all these questions——Leonardo da Vinci. You might {#blank#}3{#/blank#}what I said, but it is true.

    Leonardo was a great genius (天才). He didn't study at a(n){#blank#}4{#/blank#}. About 1,500 years ago, he lived in Italy. He had lots of {#blank#}5{#/blank#}. One of them was inventing (发明) things. One of his notebooks had drawings of a helicopter. Of course, he wasn't {#blank#}6{#/blank#}to build a helicopter with the things he had. But{#blank#}7{#/blank#}said his idea worked.

    Leonardo wasn't just an inventor. He enjoyed painting. He was one of the greatest {#blank#}8{#/blank#}of his day. When he was young, he was an excellent painter. As he {#blank#}9{#/blank#}he became more famous. Many of Leonardo's wonderful{#blank#}10{#/blank#}are still with us today, for example, the smiling woman the Mona Lisa.

    In today's world, sleep experts often say that for a better night's rest, Americans should turn {#blank#}1{#/blank#} their smart phones or iPads before sleeping. Such electronic products make the brain more {#blank#}2{#/blank#}, and then influence their sleep. But according to a latest survey, more than 90% of Americans regularly use a computer or some other {#blank#}3{#/blank#}of electronic products in the hour before bed.

    Researchers find that man-made light from some electronic products at night may reduce(减少) the brain chemicals that help {#blank#}4{#/blank#}. In the study, the researchers let volunteers read, play games and watch movies on a screen for different time while measuring {#blank#}5{#/blank#}much light their eyes received. They found that two hours of {#blank#}6{#/blank#}before a bright screen at night reduced the sleep chemical levels by about 22%.

    Then the researchers studied the college students {#blank#}7{#/blank#} often used computers at night. They got the {#blank#}8{#/blank#} results. And researchers say that may not only cause sleeplessness, but also {#blank#}9{#/blank#} the risk of obesity(肥胖症), diabetes(糖尿病) and other diseases.

    To be on the safe side, the researchers suggest that we should use computers {#blank#}10{#/blank#} than before, or turn down our screens as much as possible before sleeping.

Julie: Did you like the singing competition yesterday, Anna?

Anna: Oh, it was{#blank#}1{#/blank#}! Nelly so well!

Julie: Well, I think Lisa sang {#blank#}2{#/blank#} than Nelly.

Anna: Oh, which one was Lisa?

Julie: The one with shorter hair. I think she sang more {#blank#}3{#/blank#} than Nelly.

Anna: Yes, but Nelly dances better than Lisa.

Julie: You can tell that Lisa really wanted to win, though.

Anna: well, everyone {#blank#}4{#/blank#}to win. But the most important thing is to learn{#blank#}5{#/blank#}new and have fun.