Many flowers in our school last year and they made our school a beautiful gardenA. plant

问题补充：

Many flowers in our school last year，and they made our school a beautiful garden．

A. plant

B. planted

C. have planted

D. were planted

答案：

A. plant

B. planted

C. have planted

(答案→)D. were planted

解析：句意：我们学校去年种了很多花，它们使学校变成了美丽的花园。主语是flowers花，与动词plant种植是被动关系，所以用被动语态，结构为:be+动词过去分词；从last year得知是过去的事情，所以用were planted,故选D。