This is the most beautiful picture __________I have seen.seen这里可以填what吗

问题描述:

This is the most beautiful picture __________I have seen.seen
这里可以填what吗

到底是填which 还是that 啊 能不给出原因

which
不是填what

不能,What不能做定语从句的连接词,这里只能用which或that