Frank insisted that he was not asleep I had great difficulty in waking him up.A. whetherB.

Frank insisted that he was not asleep I had great difficulty in waking him up.
A. whether
B. although
C. for
D. so

A. whether(答案→)B. althoughC. forD. so解析：考查从属连词。although作为连词引导让步状语从句。句意为：尽管我很难叫醒他，但弗兰克却坚持说自己没有睡觉。前后句子表达“虽然??但是??”的转折语气，故选B项。whether作为连词可接名词从句表示“是否”的意思，接让步状语从句表示“不管, 无论”,与题意不符；for作为连词引导原因状语从句；so作为连词引导结果状语从句；均不合题意。选B。

就是这个解释