I just wonder why you didn’t answer my phone.—I’m sorry,( but) I a was having ameeting then

问题描述:

I just wonder why you didn’t answer my phone.—I’m sorry,( but) I a was having ameeting then
为什么用but 不用because?

I am sorry,but..是常见结构,but用来解释原因,意思就是because,但习惯上不用because.