单选题 The reason ______ he did not arrive in America as scheduled was that his flight was called off because of the bad weather.
A. when B. why C. which D. where

【正确答案】 B
【答案解析】[解析] 定语从句
[解析] 首先可以判断这句是定语从句，先行词reason在从句中作原因状语，因此应该用关系副词why来引导定语从句，故选B。