I'm sure he saw me. (must)

> He (a)   me.

Maybe he is not working today. (may)

> He (a)   today.

This app will definitely help you improve your productivity. (bound)

> This app (a)   you improve your productivity.

The economy won't probably contract again this year. (unlikely)

> It (a)   again this year.

They are likely to vote for him in the election. (probably)

> They (a)   for him in the election.

They didn't have their car, so I'm sure they didn't get very far. (cannot)

> They didn't have their car, so they (a)   very far.

They were supposed to call before 9. Maybe something's happened to them. (should)

> They (a)   before 9. Maybe something's happened to them.

They'll probably promote him after the good results. (likely)

> They (a)   him after the good results.

When she sees this mess, she will definitely be disappointed. (sure)

> When she sees this mess, she (a)   .