In the seconds after my fall I thought how nice it would be if no one had noticed.
求教各位老师,过去虚拟语气为何这样用? 主句中为何用would be而不是would have been?
你的怀疑是有道理的,严格说来应该用 would had been。
网友的句子是正确的,这是一种错综时间条件句。赵振才教授在《英语常见问题解答大词典》增订版第五版第117-119页对这种句子作了很详细的介绍。