It was amazed what she felt that he was still alive.

错误
改成：
It was amazing that she felt that he was still alive.
她觉得他还活着,真令人震惊.为什么不用what而用that？后面跟的是一个完整的从句，不缺少成分，what必须要充当后面从句的成分，而这里不缺少成分，所以应该用that楼下有人说没错，自己仔细看一下，这里的what充当什么成分呢？你会发现，既不是主语也不是宾语，压根儿没法把这个what解释清楚，因此是错的，只能用that。你是说she felt that he was still alive是完整句子，所以用that引导？是主谓宾格式吗？麻烦再说说。。。对，She felt that he was sill alive 主语 谓语宾语从句因此，句子是一个完整的结构，不需要what。