英语主谓什么时候倒装什么时候不倒装

状语短语或副词放句首表示强调时,用倒装：under no circumstances will China be the first to use nuclear weapons。In the answer to these questions lies the the key to the problem。Hardly。。。when。。。No sooner。。。than。。。Young as he is,he can solve this difficult problem。