The most important thing we should consider is the first idea he has mentioned in the sp

问题补充：

The most important thing we should consider is the first idea he has mentioned in the speech.

A. which; that

B. that; which

C. which; which

D. that; that

答案：

A. which; that

B. that; which

C. which; which

(答案→)D. that; that

解析：考查定语从句。第一个that在定语从句中作consider的宾语；第二个that在定语从句中作mention的宾语，由于先行词分别为最高级及序数词修饰，关系词用that。