I've always found laughable the idea ____ Obama is not an ideolo

I've always found laughable the idea ____ Obama is not an ideologue.
A、that
B、which
C、of
D、of which
【正确答案】：A
【题目解析】：在idea，word，fact等词后的从句一般为同位语从句，只能用that引导。同位语和定语从句的区别在于that在从句中不作成分。