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营养缺陷型

答案

参考答案：某一野生型菌株因发生基因突变而丧失合成一种或几种生长因子、碱基或氨基酸的能力，因而无法在基本培养基上正常生长繁殖的变异类型，叫做营养缺陷型。

阅读理解

In China, the traffic keeps on the right. But when you are in England, you must be very careful because the traffic drives on the left. Before you cross a street, you must look to the right and the left. In the morning and in the evening, when people go to or come from work, the streets are very busy. Traffic is the most dangerous（危险）then.

When you are in some English cities, there are big buses with two floors, you can sit on the second floor. From there you can see the city well. It’s very interesting.

小题1:In England the traffic moves ________.

A．on the right

B．on the left

C．in the middle

D．in the park小题2:When you cross a street, you must look to _________.

A．the front

B．the right

C．the left

D．B and C小题3:It is ______ to cross the streets in the morning and in the evening.

A．dangerous

B．interesting

C．easy

D．safe（安全）小题4:You can see the cities very well on the ______ floor of the bus.

A．first

B．second

C．third

D．fourth小题5:In most parts of China, the traffic are on the     .

A．front

B．left

C．right

D．back
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