问题 单项选择题 B型题

VP实验().

A.检测细菌对氨基酸的分解

B.检测细菌对糖的分解

C.两者均可

D.两者均不可

E.其他

答案

参考答案:B

解析:某些细菌可以产生一种胞外酶(明胶酶),能使明胶分解为氨基酸,从而失去凝固力,半固体的明胶培养基成为流动的液体。有的细菌可以将七叶苷分解为葡萄糖和七叶素,七叶素与培养基中枸橼酸铁的二价铁离子反应,生产黑色化合物,使培养基呈黑色。某些细菌在糖代谢过程中,分解葡萄糖产生丙酮酸,丙酮酸脱羧产生乙酰甲基甲醇,乙酰甲基甲醇在碱性环境中,被空气中的氧氧化为二乙酰,进而与培养基内蛋白胨中精氨酸所含的胍基起作用,生产红色化合物,则为VP试验阳性。

阅读理解

Ever since farmers began to grow grain, they have had to protect their crops from birds. In the 1300's, English farmers hired children to protect their crops. They were called “bird scares”. The children chased birds and threw stones at them.

Bird scares were replaced in the 1800's by scarecrows. A scarecrow is anything that is set in a field to scare birds away. Often it is a pole dressed like a person. Some farms with small fields still use scarecrows today.

Farming became big business in the twentieth century. Scarecrows could no longer protect the huge fields of grain, so farmers used poisonous chemicals on the fields. The poison made the grain bitter. The birds usually would not eat the bitter grain.

Although they can prevent crops from being destroyed by insects and birds, some chemicals can be harmful to humans. Therefore, farmers are using fewer chemicals now than they did twenty years ago. Perhaps scarecrows may be seen more often in the fields in the future.

小题1:English farmers began to hire children to get away birds since_____.

A.the twelfth century

B.the fifteenth century

C.the sixteenth century

D.the fourteenth century小题2:“Bird scares” keep birds away from crops by_____.

A.feeding them bitter grain

B.pretending to be scarecrows

C.spreading chemicals in the fields

D.chasing them and throwing stones小题3:Which statement from the passage supports the idea that scarecrows may be seen more often in the fields in the future?

A.Scarecrows could no longer protect fields.

B.They were called “bird scares”.

C.English farmers hired children.

D.Farmers are using fewer chemicals.小题4:The author's purpose is to ________.

A.give information about children who worked as bird scares

B.tell how crops have been protected from birds

C.make the readers feel sorry for birds that eat poisoned grain

D.entertain the readers with a funny story

问答题