The reason ________ I’m writing is to tell you about a party on

The reason ________ I’m writing is to tell you about a party on Saturday.
A、because
B、why
C、for
D、as
【正确答案】：B
【题目解析】：本题考查定语从句。先行词为the reason在定语从句I’m writing to you中作原因状语，故用why，选B。