存在于钙化的骨基质陷窝内的细胞为A．成骨细胞 B．骨细胞 C．骨衬里细胞 D．破骨细

There are many kinds of ants in America. One kind is very strong. People are afraid of it.

These ants move in a large group. They eat all the animals on their way. They can kill and eat elephants, and they can eat wood houses. Sometimes even people are killed by them. When the ants come, people leave their homes. But people are sometimes glad after the ants pass through, because they can see no insects(昆虫) or snakes.

小题1:Some ants in America can be very ______.

A．heavy

B．strong

C．large

D．thin小题2:People and animals are afraid of _____ in America.

A．one kind of ant

B．all kinds of ants

C．small ants

D．large ants.小题3:People have to get away from the ants because ________.

A．they can eat and kill elephants

B．they can also eat wood houses

C．they go in large groups

D．they can even kill people小题4:Where are the insects or the snakes after the ants pass through?

A．They hide themselves under the ground.

B．They have moved to other places before the ants come.

C．They can be killed and eaten up by the ants.

D．They were killed by people.小题5:Which is the best title for the story?

A．Ants

B．American Ants

C．A strong Ant

D．Animals

书面表达。

     现在有很多人，尤其是青年人，喜欢骑自行车旅行，但仍有不少人喜欢坐火车。其实，自行车和

火车均有不足之处。请你以Travel by Bike or Train为题写一篇100-120词的短文。介绍各自的优缺点。

     自行车的优点：方便( convenient)、经济(economical)、有益于健康。

     火车的优点：快速、省时、乘坐舒适。

     各自的缺点：自行车速度慢，不能用来进行长途旅行。火车不方便，没有铁路的地方不能去

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无菌实验室使用前应以紫外线消毒（）。

A.10min

B.20min

C.30min

D.5min

E.40min

银行存款日记账的借方一定是根据收款凭证登记的，贷方一定是根据付款凭证登记的。( )

柴油机的高、中、低速如何区分？