阅读下列短文，从每题所给的四个选项（A、B、C和D）中选出最佳选项。

D

    Jack is a 13-year-old boy.

    One day, his father asks him, "How many letters are there in the alphabet(字母表)?"

    "24." He says.

    "24?" His father asks loudly, "Are you sure?"

    "Sorry, I don't know." Answers the son.

    "You don't know? You are in school for 7 years and you don't know how many letters there are in the alphabet?" The father is very angry(生气的).

    His son says, "No. But let me ask you a question, dad. You often go to the post office(邮局). Please tell me how many letters there are in the post office."