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