It is that he has been addicted to the drugs and has difficulty quitting it.
A. obviously
B. apparently
C. possibly
D. likely
网友回答
A. obviously
B. apparently
C. possibly
(答案→)D. likely
解析：考察形容词作表语。形容词可用在be动词后作表语。副词一般用在实意动词后做状语，句中is后应用形容词作表语，ABC选项都是副词，故只能选D，很可能的，既能做副词，又能做形容词。