As crossing

While you cross

While crossing

Cross

这题考查时间状语从句的省略式，当主从句的主语一样时，可以省略从句的主语和be动词，这题的while crossing就省略了you are，句意是：当你过马路时，别忘了两边看看。选C。

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。

If you see things in a negative light, you will find faults everywhere and problems where there are really          .

none

some

many 

nothing

考查代词辨析。句意：如果你用消极的眼光看待事物，你会发现到处都是问题。A. none没有任何东西；B.some 一些；C.many 许多；D.nothing 无事；无物。此处指没有问题的地方也有问题·。故选A项

Dr.Rowan,           secretary resigned two weeks ago, has had to do all his own typing.

whose

of whom 

of which

which

考查定语从句。句意：罗文博士的秘书两周前辞职了，他只能自己打字。          secretary resigned two weeks ago是非限制性定语从句，修饰Dr.Rowan, 引导词在从句中作定语，表示“Dr.Rowan's”，表示“......的”，应用关系代词whose引导该从句。故选A项。