I've redone this math problem at least twenty times, but my answer is wrong according to the answer key. The answer in the book ___ be wrong!
A.should
B. have to      
C.must 
D.could

You ___ worry so much. It doesn't do you any good. Either you get the job, or you don't. If you don't, just apply for another one. Eventually, you will find work.
A.can't 
B.don't have to
C.shouldn't
D.may not

Do you always have to say the first thing that pops into your head. ___ you think once in a while before you speak?
A.Can not
B.Don't
C.Can't
D.Why

You ___ forget to pay the rent tomorrow. The landlord is very strict about paying on time.
A.couldn't
B.don't have to
C.mustn't
D.needn’t

The machine ___ on by flipping this switch.
A.could be turning
B.can be turned
C.may turn
D.need turning

Mr. Brown is bored__________ doing the same job for too long.
A.at  
B.in 
C.of 
D.with

When it turned out that Alice ___ to hospital before July, I phoned the agency  to cancel the bookings. I didn’t want to risk losing the money, in case she did.
A.needed have gone
B.might have to go
C.could have gone
D.needed to have gone

You ___ take along some cash. The restaurant may not accept credit cards.
A.had better
B.has to
C.can
D.dare

At first, my boss didn't want to hire Sam. But, because I had previously worked with Sam, I told my boss that he ___ take another look at his resume and reconsider him for the position.
A.has to
B.must 
C.ought to
D.will

If I had gone white water rafting with my friends, I ___ down the Colorado River right now.
A.would be floating
B.would have floated
C.would float
D.would have been floated