PERPLEXING : EXPLICABLE :: ZEALOUS :
A. diligent
B. unyielding
C. indifferent
D. incorrigible
Something that is PERPLEXING is difficult to explain, or inexplicable. EXPLICABLE describes something that can be explained. Thus, these two words are antonyms (opposites). Someone who is zealous cares very strongly about something. In contrast, someone who is indifferent does not care.