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
网友回答
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。