The letters_____on your desk yesterday, but you didn't read them

The letters_____on your desk yesterday, but you didn't read them at all.
A、were put
B、being put
C、put
D、have put
【正确答案】：A
【题目解析】：本题考查动词的用法。句意：那些信昨天就放在你的桌子上了，但你根本没有读它们。本句中有but连接前后两个句子，因此前面半句是一个完整的句子，缺少谓语动词，且动作发生在昨天，动词要用过去式。letters和put之间是被动关系，要用被动语态，所以要用were put。故本题选A。