It worries the couple ____ their daughter is eating less and less these days
问题描述：
It worries the couple ____ their daughter is eating less and less these days
A how B when C that D because
请详细分析每个选项,
我想问为什么不是D呢
答
It形式主语,that引导主语从句.
用because的话很奇怪,it不知道是什么东西,如果可以用because,同理可以用when.
而how完全不沾边.