用括号内所给单词的适当形式填空。
1.They failed ________(get)to the top of the hill at last.
2.The classroom must ________(keep)clean every day.
3.What shall we do if it ________(rain)tomorrow?
4.Trees ________(be)often ________(plant)in spring.
5.You needn't ________(worry)about your son. He's OK.
1.to get 2.be kept 3.rains 4.are;planted 5.worry