The most important thing we should consider is the first idea he has talked about in the

问题补充：

The most important thing we should consider is the first idea he has talked about 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：这题考查定语从句的用法：第一空先行词是最高级 the most important thing，所以用that引导定语从句，第二空还是填that，，因为先行词被序数词the first修饰，选D。