按要求完成下列句子，每空一词。
1.We bought a piano last term.(改为被动语态)
A piano ________ ________ by us last term.
2.Penicillin was discovered by Alexander Fleming.(改为一般疑问句)
________ Penicillin ________ by Alexander Fleming?
3.The books were written by Mr. Li many years ago.(改为否定句)
The books ________ ________ by Mr. Li many years ago.
4.Their homework was handed in yesterday.(对画线部分提问)
________ ________ their homework ________ in?
15.We didn't grow vegetables in the garden last year.(改为被动语态)
Vegetables ________ ________ in the garden by us last year.
1.was bought 2.Was；discovered 3.weren't written
4．When was；handed 5.weren't grown