题干

为探究食品腐败的原因和细菌生存的条件,某生物小组取经过消毒的、大小相同的锥形瓶甲、乙、丙三个,按如表要求进行处理.下列说法正确的是:

处理方式

加入物质

50毫升灭菌牛奶

50毫升灭菌牛奶

50毫升灭菌牛奶

瓶口处理

不作处理

不作处理

用消毒棉球塞住

温度

25℃

5℃

25℃

请据表分析:处理中包含了多少组对照实验,变量是什么?(   )

A:2组,温度、空气

B:2组,温度、消毒棉球

C:2组,温度、细菌

D:3组,温度、消毒棉球、细菌

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答案(点此获取答案解析)

C

同类题4

阅读理解

    A farmer grew some vegetables in his garden. One day his wife was ill and he had no money. He had to sell some cabbages and carrots in the market. The next morning he took two baskets of vegetables to town, but it was raining hard that afternoon and there were few people in the street. When his vegetables were sold out, it was dark. He bought some medicine and hurried to his village.

    On his way home he saw a person lying on the ground. He placed his baskets on the ground and was going to help the person to get up. At that time he found it was a dead man and there was much blood on his body. He was so afraid that he ran away quickly, without taking his baskets.

    The next afternoon the farmer was sent to the police station. Having shown the baskets, an officer asked, “Are these yours? ” “Yes, sir. ” The farmer answered timidly(胆怯地). “Have you killed the man?” “No, no, sir.” The farmer said in a hurry. “When did you see the dead man?” “About seven last evening. ” “Did you see who killed the man?” “No, sir. ” The officer brought out a knife and asked, “Have you seen it yet?” “No, sir. ” The officer became angry and told the policemen to beat him up and sent him into prison.

    That evening the officer went on trying. Pointing to the knife, he asked again, “Have you seen it yet?” “ yes, sir.” The officer was happy and asked, “When and where?” “I saw it here this afternoon, sir.”