The reason matters most in his failing the English test is he pays little attention to s

网友回答

A. why, that
(答案→)B. that, that
C. which, because
D. what, because
解析：考查定语从句和表语从句。the reason后面的句子不是对它的补充，因而不是同位语从句，而是定语从句，The reason是先行词，定语从句缺少主语，用that或which；排除A、D；is后是表语从句，用that引导。故选B。