人体感染旋毛虫是由于（） A.吞入感染性虫卵 B.误食幼虫囊包 C.幼虫从皮肤钻入

— What should I do with this passage?

—  _____to the main idea of each paragraph.[ ]

A. Finding out

B. Found out

C. Find out

D. To find out

单项选择。

How many _______ can you see? [ ]

A. goat

B. goates

C. goats

D. a goat

当电源频率增加后，分别与灯泡串联的R、L、C3个回路并联，与（）串联的灯泡亮度增加。

A.R

B.L

C.C

D.R和L

E.R和C

支（拱）架的安装有何要求？

This rare bird has become（）

A.an endangered specie

B.endangered species

C.endangering species

D.an endangered species