在英语越来越普及的21世纪，英语水平的高低已经成了大学生是否能找到好工作的评定标准。为帮助大学生掌握权威的英语知识。特提供以下资料：
特定结构和句型中的时态
1.
This(That/It) is the first (second…) +名词+定语从句
This(That/It) is the only (last) +名词+定语从句
This(That/It) is the +形容词最高级+名词+定语从句
Examples
This is one of the rarest questions that ___ at such a meeting.
A. has ever been raised B. is raised C. are raised D. have ever been raised
There was a knock at the door, it was the second time someone ___ me that evening.
A. had interrupted B. would have interrupted C. to have interrupted D. to be interrupted
2.
It is /has been + 时间段 since +从句(一般过去时)
It will be +时间段before +从句(现在时)
It was +时间段before +从句(一般过去时)
It is likely /unlikely that +从句(一般将来时)
Examples
It ___ 2 weeks since she fell down the stairs, but you can still see the bruises.
A. was B. is C. will be D. were
Last night a man escaped from prison. It was a long time ____ the guards discovered what had happened.
A. since B. when C. before D. that
3.
“祈使句+and”结构中, and 引导的并列分句谓语动词用一般将来时。
Hardly/scarcely…when, no sooner…than句型中主句常用过去完成时，从句用一般过去时。
Examples
___ when she started complaining.
A. Not until he arrived
B. Hardly had he arrived
C. No sooner had he arrived
D. Scarcely did he arrive
Turn on the radio or open a magazine and you ___ advertisements showing happy and balanced families.
A. are often seeing B. often see C. have often seen D. will often see
副词的位置
在时态测试中，根据某些副词在句中的特殊位置这一特点，也有助于判断选项的正误。 频率副词always, often, frequently, seldom, never, ever, usually , rarely, occasionally, no sooner, hardly, scarcely等以及just, shortly等其他副词必须放在助动词、情态动词或be动词与实义动词之间。在省略结构中，这些副词必须放在助动词、情态动词或be 动词之前。
Examples
We ___ our breakfast when an old man came to the door.
A. just have had B. have just had C. just had had D. had just had
San Francisco is usually cool in the summer, but Los Angeles ____.
A. is rarely B. rarely is C. hardly is D. is scarcely
时态一致
从句谓语动词时态受主句谓语动词时态限制，主句谓语动词是现在时或将来时， 从句时态根据需要选择;主句谓语动词是过去时，从句通常也用过去时。这是四级语法测试重点。如：主句谓语动词是过去时，则
1)主从句动作同时发生，从句did 或was/were doing.
2) 从句动作发生在主句动作之前，从句had done.
3)从句动作发生在主句动作之后，从句would do.
Examples
After searching for half an hour, she realized that her glasses ___ on the table all the time.
A. had been lying B. had been lain C. have been lying D. were lain
Exception (例外)
如果从句中所表示的是一个客观事实或科学真理，从句谓语动词不受时态原则限制，只能(永远)用一般现在时，通常根据常识就可以确定答案。
Our teacher has a strict rule. She said yesterday that all the students ___ to class on time.
A. came B. might come C. must come D. must have come