How to use "concentrate" in a sentence

This one was very exciting, but Sala couldn't concentrate

You were excited and you couldn't concentrate on anything else, but you were also a tiny bit afraid

She had to concentrate on the indisputable facts

He returned and tried to concentrate on his examination notes, but without success

I remembered how I could not concentrate that morning, hardly a month before, and how I had stopped work to get my newspaper from the newsboy