In response to a question asking about a cause/reason, it is possible to give a short answer by mentioning the reason/cause only, omitting the "result" part.
A: どうして 学校を 休んだのですか。
Why were you absent from school?
B: →かぜを ひいたからです。
It's because I had a cold.
A: あなたは どうして 肉を 食べないのですか。
Why is it that you don't eat meat?
B: →きらいだからです。
It's because I dislike meat.
Lesson 10-7「ひこうじょうへ 友だちを むかえに 行きますから、休みます。」
I'm going to the airport to meet a friend, so I'll be absent.