_______ for your laziness，you could have finished the assignment by now.
正确答案： A
本题解析：
句意： 要不是你懒惰， 到现在你就能完成任务了。 本题是一个省略 if 的虚拟条件句， 主句用 could have done表示与过去事实相反，条件从句应用 had done形式， had 要提前构成倒装。
The professor asked a question, and David ________ a good answer.
He would have given you more help, if he ________ so busy.
After months of voyage, Columbus arrived in ______ later proved to be a new continent.
It rained hard yesterday, ______ prevented me from going to the park.
It is important to ________ your skin from the harmful strong sunlight.
He was ______ to withdraw from running for the presidency.
The two girls competed with each other ______ the highest mark.
If the operation ________ carefully prepared, it would not have been successful.