题干

亚洲人体内普遍缺乏乳糖酶,造成饮用牛奶后出现肠胀、腹胀、腹泻等不良症状.下列有关乳糖酶的叙述,正确的是(   )

A:若人体消化道细胞不能产生乳糖酶,则该细胞也不能产生ATP

B:人体缺乏乳糖酶的根本原因一定是缺乏控制该酶的基因

C:乳糖酶只能在细胞内发挥催化作用,属结构蛋白

D:一定条件下,乳糖酶可将一分子乳糖分解为一分子半乳糖和一分子葡萄糖

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D

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    Look at the light and beautiful snowflakes (雪花) falling. Ever wanted to hold them in your hands? They are always lost when they meet your hands.

    Well, this isn't just a problem for you. It was a problem for Wilson Bentley, too. In the 1870s, Wilson Bentley was just a teenager. His family lived in a small town in northeast America. Winters there were long and hard. Bentley's mother was once a school teacher. She taught him at home. Bentley didn't go to school until he was 14. He was a quiet boy, and loved reading his mother's books. But he was interested in his mother's microscope (显微镜). When the other boys were playing with balls, little Bentley was studying things like drops of water, flowers and snowflakes.     

    Bentley loved watching snowflakes. For the next two years, young Bentley spent many winter days in a cold room watching these ice crystals (晶体) under his microscope. The boy thought they were beautiful enough for him to start to draw pictures of them. But there were so many snowflakes that he couldn't draw them all.

    How could he keep their beauty all the time? Bentley thought of buying a camera.

    The boy and his mother asked his father to buy one. But, his father didn't agree. He thought the whole thing was a bad idea. He thought the only thing a farmer should do was farming.

    But finally Bentley did get a camera. For more than a year he tried to take pictures of snowflakes. On January 15, 1885, during a snowstorm, Bentley took the first ever photo of an ice crystal with his camera. “It was the greatest moment of my life,” Bentley said later.

    For 13 years, Bentley worked quietly and took thousands of photos of ice crystals. Later he became famous as “Snowflake” Bentley.