关于what it is that的疑问

问题描述:

关于what it is that的疑问
The search for what it is that ignites the human spirit,overcoming the unexpected and discovering the unknown.
这句话的意思是:探索是什么点燃了人类精神,克服意想不到之事,发现未知世界...
what it is 做的是什么成分,为什么不能改成what ignites...

what ignites 也对,只不过这里用了强调句式,即it is what that ignites...在这里what it is 相当于一个形式主语