I failed in the final examination last term and only then _________ the importance of studies．

I realized

I had realized

had I realized

did I realize

_________ environmental damage is done, it takes many years for the ecosystem to recover．

Even if

If only

While

Once

Little _________ about his own safety, though he was in great danger himself．

does he care

did he care

he cares

he cared

_________ for the free ticket, I would not have gone to see the film so often．

If it is not

Were it not

Had it not been

If they were not

Not a single song _________ at yesterday’s party．

she sang

sang she

did she sing

she did sing

_________ can you expect to get a rise．

With hard work

Although work hard

Only with hard work

Now that he works hard

So difficult _________ it to live in an English-speaking country that I was determined to learn English well．

I have felt

have I felt

I did feel

did I feel

_________, I have never seen anyone who’s as capable as John．

As long as I have traveled

Now that I have traveled so much

Much as I have traveled

As I have traveled so much

My sister had a cold last week, so _________．

I had

I did

had I

did I

Only if he helps us _________．

we may succeed

we succeeded

can we succeed

we can succeed