It's a bad habit ____after dinner.

1.答案：D.
2.翻译：饭后跑步是一种坏习惯.
3.
1）这是一种英语中最常见的句型.
It be + 名词/形容词 + (for/of) sb to do sth.
对某人来说做某事是什么样的.
2）句型中,it是形式主语,不定式才是真正的主语.
如：It's time (for you) to have dinner.
It's a waste of money to buy such an expensive car.
It's difficult to finish the work in five minutes.
It's kind of you to help me.

这个答案顺口一读就得出来了呀
应该是一个固定搭配吧。
It is good for your health .这样吧

D 动词不定式短语作状语