Read these sentences and fill in the gaps with 'could', 'can', 'couldn't', 'can't'.
1. Adam and his mother
open the door because it was locked.
2. Before the nuclear disaster in the 1980's, people
grow everything in their gardens.
3. Steve
solve this problem now. He needs time.
Mary was cooking a salad at 7 o'clock yesterday.
They were argueing when I entered
Bill was surfing the net when the dootbell rang.