题干

1953年,沃森和克里克建立了DNA分子的结构模型,于1962年获得诺贝尔生理或医学奖.关于DNA分子双螺旋结构的特点,错误的说法是(  )

A:DNA分子由两条反向平行的链组成

B:脱氧核糖和磷酸排列在外侧

C:碱基互补配对构成DNA的基本骨架

D:腺嘌呤总是与胸腺嘧啶配对

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答案(点此获取答案解析)

C

同类题5

阅读理解

    Every year many young people leave school for a few weeks or months and enjoy an unusual type of educational program. They learn new skills by living in a different country and doing unusual jobs. There are several organizations. They help students to find the experience they are looking for. The table below shows a few possibilities for students.

Country

Job

Time

Description

India

Teaching young children

One month

·Teaching music and dance

·Helping children learn how to communicate

Ghana

Health care work

Two months

·Seeing how doctors work in a less developed country

·Helping care for patients

Thailand

Saving elephants

Three weeks

·Cleaning elephants

·Helping train elephants

New Zealand

Teaching Chinese

Six weeks

·Helping adults learn Chinese

·Spreading Chinese culture

    One interesting possibility is helping elephants in Thailand. Most people think of elephants as animals in zoos. In fact, many elephants in Thailand are no longer kept in cages. Now, hundreds of them are homeless. They don't have owners to care for them. Although they may look well, they are often in poor health and don't have enough to eat.

    One center in Thailand cares for these elephants. It gives them a safe and natural living space. When they are at the center, they stay in a building but are free to walk around. Students come from all over the world to help here. The student helpers work with the elephant keepers. These keepers train the students in caring for the elephants. In the morning, they go to the forest together and lead the elephants to the center. They clean them and give them food. In the afternoon. They take the animals back into the forest for the night. Helping at the center is interesting and the young people learn a lot.