He was much more thorough in his studies than the rest of his class and it was for this reason ______ he made such great progress.
A、why
B、how
C、that
D、for
【正确答案】：C
【题目解析】：译文：他在学习方面比班里其他同学都认真细心，正因为这个原因他才取得了如此大的进步。此句是一个由and连接的并列句。后一个分句中，句子的各个成分都完整，for this reason为原因状语，所以这并不是一个由why引导的定语从句而是It is...that强调结构。答案为C。
