I can’t look up the new words because I don’t have a dictionary.

If I had a dictionary, I could look up the new words. (conditional type 2)

The scientists are studying the problem carefully.

The problem are being studied by the scientists carefully.(Passive)

We can’t look up the new words because we don’t have a dictionary.

If we had a dictionary, we could look up the new words.(conditional type 2)

They have not seen such a beautiful picture before.

This is the first time they have seen such a beautiful picture.(phrase )

If you don’t study hard, you will fail in the exams.

Unless you study hard, you will fail in the exams.(conditional type 1)

Unless you go out, I will call the police.

If you don't go out, I will call the police.(conditional type 1)

Unless I have a quiet room, I will not be able to do any work.

If I don't have a quiet roon, I will not be able to do any work.(conditional type 1)