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问题 单项选择题

植物体细胞杂交是利用不同物种的两个体细胞融合成一个杂种细胞的过程。该过程是指（）

A.不同植物的精子与卵细胞的融合

B.不同植物的原生质体的融合

C.完整的两个体细胞的融合

D.植物花粉细胞的两两融合

答案

参考答案：B

阅读理解

任务型阅读。

     My name is Dave. I have two good friends. On Saturdays we often go to see the animals in the zoo.

Tom likes pandas because they're kind of shy. He likes Ling Ling best. Ling Ling is three years old now.

Tom often goes to see her. Mary likes to play with dolphins. There are two dolphins in the zoo. They're

friendly to people. My favorite animals are lions. I think they're smart. But Mary doesn't like them. She

says lions are too scary. We have a little dog. Its name is Bargo. It's black and white. Bargo often goes

with us to the zoo. It's cute. We all love it very much.

根据短文内容回答下面的问题，每空一词。

1. When do they often go to the zoo?

    They go to the zoo _____ _____.

2. How old is Ling Ling?

    She is_____ _____ old.

3. Why does Mary like dolphins?

    Because they're _____ _____ people.

4. What kind of animal is Bargo?

    Bargo is a _____. It's _____.

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单项选择题

潜伏性感染是指

A．病原体侵入人体后，只引起轻微症状

B．病原体侵入人体，引起免疫反应，不出现症状

C．病原体侵入人体发生免疫反应，不出现症状

D．病原体与入体保持永久平衡，不出现症状

E．病原体与人体相互作用，保持暂时平衡，当人体防御机能减弱时，可引起疾病
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