He sang and danced as if he ________(be) the only person in the world?
答案是were,请问为什么不用had been
as if 虚拟的规则：与过去事实相反，从句谓语动词用had done.
【答】如果主句的谓语动词是过去时态，as if / as though 从句的谓语动词可以用过去完成时也可以用一般过去时表示与过去事实相反的情况。例如：
He was singing as though he hadn’t had (didn’t have) a care in the
world. 他唱着歌，好像他在人世间没有忧虑。（摘自《薄冰英语惯用法词典》p.83）
