If you want to catch the first bus you'd better         for the bus station immediately.

set up

set about

set down

set off

考查动词短语辨析。句意：如果你想赶上第一班公交车，你最好马上动身去车站。A. set up建立；B. set about开始做.....;C. set down 记下；D. set off 出发，动身。结合上文If you want to catch the first bus you'd better可知此处指“动身，出发”，应用set off。故选D项。

It was along the Mississippi River _________ Mark Twain spent much of his childhood.

how

which

that

where

此处构成It was...that...强调句式，句中强调了介词短语along the Mississippi River。故选C。

So difficult __________ it to work out the problem that I decided to ask Tom for advice.

 I did find 

did I find

 I have found  

have I found

句子使用的基本句式为so…that…结构。按英语语法，当该结构的so…置于句首时，其后的句子(主句)要用倒装语序，如：So loudly did he speak that even people in the next room could hear him. 他讲话声音那么大，隔壁屋里的人都听得见。

The teacher was so pleased with the progress that I had        in my study this term that she sent me an English-Chinese dictionary.

made

had 

kept

graded

考查动词辨析。句意：老师对我在这学期在学习上取得的进步非常满意，寄给我一本英汉词典。分析可知hat I had        in my study this term 应是之前名词the progress的定语从句，先行词在从句中属于固定结构make progress“取得进步”的宾语。故选A项。

Great amounts of water            poured into the river from the factories two years ago.

was

were

has been

have been

考查时态和主谓一致。句意：两年前，工厂将大量废水排入河中。根据two years ago 可知，句子使用一般过去时。....amounts of修饰不可数名词作主语时，谓语动词用复数形式，即谓语动词与amounts保持数的一致。故选B项。

People           about what our future will look like for thousands of years.

have been wondering

wonder

wondered

will wonder

考查动词时态。句意：数千年以来人们一直想知道我们未来是什么样子。根据时间状语 for thousands of years可知，描述从过去开始一直持续到现在的动作，用现在完成进行时。故选A项。