【题目】He tried his best to solve the problem, ____ difficult it was.
A. however B. no matter
C. whatever D. although
在线课程【答案】A
【解析】试题分析：考查让步状语从句。句意：无论问题有多么棘手，他都会竭尽全力去解决它。疑问词+ever既可以引导名词性从句，也可以引导让步状语从句，引导让步状语从句时相当于no matter+疑问词。difficult是形容词，修饰形容词或副词应该用how或however，排除C；B项后缺少how，排除B；although后跟句子，排除D，故选A。