Researchers have come to the conclusion over the last 5 years ________ teens need to sleep until about 8∶00 the next morning．

when

what

whether

that

No wonder he speaks Spanish as fluently as a native speaker．He ________ to Spanish for some ten years．

exposed himself

has been exposed

exposes

was exposed

The bus was held up by the snowstorm, ________ causing the delay．

as

however

thus

and

In the eyes of ________ local people, the young soldier is ________ second to none, for he managed to save ________ old lady at the risk of his life．

/;/; the

the; the; the

the;/; an

/; a; an

We ________ last night, but we went to the concert instead．

must have studied

might study

should have studied

would study

Talking about buying cars, I prefer a car less than 100,000 yuan to ________ over the amount．

this

it

that

one

If ________ unsolved, this may lead to more serious problems．

making

remained

left

taking

The new movie ________ to be one of the biggest money-makers of all time．

pretends

agrees

promises

declines

Unfortunately, the element Madam Curie devoted all her life ________ her death．

to caused

causing

to be caused

to causing

When exposed to stress, in ________ form, all of us react both chemically and physically．

whichever

whatever

however

whenever