A. put B. putting
C. to put D. to be putting
但是请注意，类似下面这样的题目情形有所不同，所填部分为目的状语（用不定式，即答案选B）：
(18) ______ French well, she went to France to live with his cousins.
A. Study B. To study
C. Studying D. Having studied
(19) _____ late in the morning, Mr. Smith turned off the alarm.
A. Sleep B. To sleep
C. Sleeping D. Having slept
(20) ______ the flies out, we had to shut all the doors and windows.
A. Keep B. To keep
C. Keeping D. Having kept
(21) ______ their service, the workers of the hotel are active in learning English.
A. Improving B. To improve
C. Improve D. Having improved