用所给动词的适当形式填空。
1.Listen! How wonderfully the girls _________ (sing)!
2.Simon will leave here if he _________ (finish) the work tomorrow.
3.________ you ________ (go) to the World Park in Beijing next week?
4.—What did you do last night?
—I _________ (write) a letter to my parents.
5.The zookeeper told them __________ (not leave) litter there.
