答案：C

题目分析：考查however引导的让步状语从句：句意： --无论这有多难，我都会尽力把它做好的。however引导的让步状语从句结构是However+adj/adv+主谓，选C。

点评： however引导的让步状语从句也可以用no matter how引导，但是要注意结构顺序：no matter how 或However+adj/adv+主谓，No matter what或whatever后面一般接名词。