May - might - can - should - must, etc.
1/ If they fire part of their staff, he --- lose his job.
2/ That ring looks so expensive, it --- have cost him a fortune.
3/ Really, you --- not worry so much...
4/ I'm quite certain they --- have done that intentionally!
5/ He --- be honest and tell them the truth!
6/ You --- park here, as it's totally forbidden...
7/ It was so dark, he --- not have seen her...
8/ Do you think you --- do that for me?
9/ He --- criticize you all the time...
10/ I think she --- help you...