用括号内所给词的正确形式填空。
1. Sam bumped his head yesterday, so he ________ (not can) sleep well last night.
2. The monster wanted to eat the birds, but the birds ________ (fly) away.
3. I couldn’t speak English then. But I ________ (can) speak English now.
4. — What did you do in the park?
— I ________ (learn) to ride my bike.
5. — How many hours did you ________ (spend) in the zoo?
— I spent six hours.