I couldn't make the salad.
I could make the salad.
He couldn't play soccer.
He could play soccer.
You couldn't remember his name.
You could remember his name.
I could understand that class.
I couldn't understand that class.
We could drive all night.
We couldn't drive all night.
I shouldn't work out.
I should work out.
He shouldn't tell the truth.
He should tell the truth.
She could buy the ticket.
She couldn't buy the ticket.
They shouldn't fire him.
They should fire him.
She shouldn't study Chinese.
She should study Chinese.
You shouldn't go home.
You should go home.
You shouldn't eat more vegetables.
You should eat more vegetables.