I had dinner 和 I was having dinner 的区别

问题描述:

I had dinner 和 I was having dinner 的区别
这道题是这样的
---I called you yesterday evening,but there was no answer.
---Oh,I am sorry I _____ dinner at my friend's home.
A.have B.had C.was having D.have had
为什么选c 为什么不选B

这里的意思是说;我给你打电话,但是你怎么不接?哦,对不起,当时我正在吃饭.是强调吃饭的进行中,所以才没有接到电话,因此选c.
b选项则只是单纯的表达了“我昨天在朋友家吃饭”的意思.