He ________ find a good solution to the problem yesterday.
could
We ________ use plastic bottles because they're reusable.
should
We ________ throw plastic in the street, we should recycle it.
shouldn't
I ________ believe how quickly he finished the project.
can't
They ________ play the online game because the server was down.
couldn't
I ________ remember where I put my keys this morning.
couldn't
You ________ leave the lights on when you leave the room.
shouldn't
You ________ waste water while brushing your teeth.
shouldn't
You ________ find a lot of information in the dictionary.
can
They ________ use more wind power to generate energy.
should
I ________ go to the park today because it's raining.
can't
She ________ hear the alarm because she was wearing headphones.
couldn't
We ________ use more solar power to help the environment.
should
He ________ send an email if he doesn't have internet access.
can't
She ________ attend the meeting yesterday because she was sick.
couldn't