They lost their way in the forest,and_____made matters worse was that night began to fall

D
此题第一个关键点是 连词 and ,它连接了两个句子.横线出现再第二个句子中,我们分析第二句_____made matters worse was that night began to fall.此句中的谓语动词是 was,那么was前面就应该是主语,_____made matters worse,所以此句子就是一个主语从句,而从句中又缺少主语,所以我们要用what 来引导.
that 引导主语从句时：不充当成分,不能省略,没有实际意思.