Choose the right verbs to complete the sentences.

Choose the correct option.

I [couldn't|can't|wasn't able to] understand the grammar rule in our student book. It is too difficult!

Mary [can't|isn't able to|couldn't] understand the foreigner because she didn't speak his language.

She looked for her glasses for hours but she [was able to|is able to|can] find them in the end.

[Am I able to|Was I able to|Can I] borrow your umbrella? It's raining.