They lost their way in the forest and this

题目

They lost their way in the forest and this
made matters worse was that night began to fall.
this处能用what吗?
如果用what怎么改?

答案

本来就该用WHAT,用WHAT指代night began to fall
而且还有一个固定用法就是 WHAT'S WORSE意为更糟的是……