Question

—Why do you look so puzzled?
—Oh，I ________ over a most difficult maths problem.

A．thought	B．have thought
C．am thinking	D．think

Answer 1

C

考查时态。句意：——为什么你看上去这么困惑？——哦，我正在思考一道数学难题。根据问话者说的“look so puzzled”可知，“思考难题”这一动作正在进行当中，故选C。