Question

____these trees were planted last year ?A who B whom C by whom D by who

Answer 1

选择C。这道题目询问的是被动语态动作的执行者，相当于：派判宴
Who planted these trees last year?
但是这个题目是有问题的，既然是疑问句，问句的句型要出来，疑问词相当于火车头，后面的问尘银句句型相当于火车车厢，我们常说物以类聚，也就是所谓的Birds of a feather flock together. 火车头的后面绝对不会拖公共汽车或卡车的车厢，一定是拖火车的车厢，冲余否则就会出轨或拖不动。所以这个句子要把were提到these trees的前面去，写成：
By whom were these trees planted last year?
除非这个句子是从属于另一个句子的名词性从句，我们才可以把疑问词放句子的中间，引导从句，后面用陈述句的语序，也就是：
I don't know by whom these trees were planted last year.
希望我能帮助你解疑释惑。

Answer 2

答案选C噢，祥银笑不看空格地方，整个搏槐句子是完整的，were planted 是被动语态，主语是trees，用by whom 来表示“由谁”，整个句子相当于：who planted these trees last year？如果帮助到你，请采纳谨含

Answer 3

C