单选题 Running a marathon is an ______ task, taking months of both physical and mental preparation and training before actually running a grueling 26.2 miles.

A、 (A) arduous
B、 (B) ambiguous
C、 (C) involuntary
D、 (D) eloquent
E、 (E) overt

【正确答案】 A

【答案解析】The context of the sentence indicates that running a marathon is quite challenging and takes a lot of preparation. Arduous means "difficult or demanding great effort," which best fits the context of the sentence.