1. _________ directly with most metals to form compounds called carbides.
A. Carbon reacting
B. Carbon reacts
C. The reaction of carbon
D. When carbon reacts
答案：B
分析：从句意来看，called在这里不是谓语动词，而是分词做后置定语：…… which are called carbides.空格中缺主语和谓语，选B.
参考译文：碳直接跟大部分金属反应而形成碳化物的化合物。
2. Meteorites are slowed down by Earth's atmosphere， but if they are moving _________， they can form a crater on impact.
A. enough fast
B. fast enough
C. so fast enough
D enough are fast
答案：B
分析：enough的用法，固定顺序：adj.+enough
参考译文：陨石受地球大气阻挡而慢下来，但如果他们移动的足够快，他们能在撞击后形成一个大坑。
3. Located at the upper end of each________ an adrenal gland， an integral part of the endocrine system.
A. kidney which is
B. kidney is
C. kidney being
D. kidney
答案：B
分析：该句为简单句，而且使用了倒装形式，原句为：An adrenal gland， an integral part of the endocrine system is located at the upper end of each kidney.
参考译文：肾上腺是内分泌系统的一个完整的部分，它位于肾的上端。
4. About 75 percent of all cadmium is used for cadmium plating of _________ such as iron and steel.
A. easily corroded metals
B. metals are easily corroded
C. corroded metals that easily
D. how easily metals corroded
答案：A
分析：B中的are多余，否则句中出现两个谓语，错;C中的that引导定语从句，而从句缺谓语，错;用法错误，of后一般接名词。
参考译文：75%的所有镉金属都用来对类似铁、钢的容易腐蚀的金属进行镉镀膜了。
5. An atom is a basic structural unit of matter， the smallest particle of an element _________ into chemical combination.
A. that can enter
B. can it enter
C. when entering it can
D. that enters can
答案：A
分析：that引导定语从句，element为先行词。the smallest particle of an element 是 a basic structural unit of matter的宾语同位语。
参考译文：原子是物体的基本结构单元，是元素形成化学组合特性的最小的颗粒。