—Why did Mike ignore (不理睬) me completely when I said hello to him?
—Oh, he was keeping ________ a problem.
A.think about B.to think about
C.to thinking about D.thinking about
—Why did Mike ignore (不理睬) me completely when I said hello to him?
—Oh, he was keeping ________ a problem.
A.think about B.to think about
C.to thinking about D.thinking about
D