They lost their way in the forest, and（ ）made matters worse was

They lost their way in the forest, and（ ）made matters worse was that night began to fall.

it

what

that

which

本题考查的是主语从句的连接代词的使用。

and后为主语从句，缺少主语成分，需使用what引导，故选择B选项。

句意：他们在森林里迷失了方向，更糟的是夜色开始降临。