The accident that happened at an oilfield____ the southeast coast of the U.S.A has caused great damage to the environment.
Had your father seen the doctor earlier, he ___.
Tom’s uncle must be an engineer, ___?
He ___ on the grass, looking at the clouds in the sky.
His mother ___ a lot of silkworms last summer.
You don’t __ to go there if you have no time.