He would have given you more help, if he ________ so busy.
正确答案： B
本题解析：
本题考察与过去事实相反的虚拟语气。
The professor asked a question, and David ________ a good answer.
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.
The furniture in her bedroom is quite different from ________ in the living room.