After his operation, the old man was back _ and he began to take exercise as usual.
A. at his feet
B. to his feet
C. in his feet
D. on his feet
网友回答
A. at his feet
B. to his feet
C. in his feet
(答案→)D. on his feet
解析：
试题分析:考查固定短语。根据句中After his operation和take exercise as usual.可以判断应该是病后恢复，短语on his feet可以指“病后复原”，所以D选项正确。句意：手术后，这个老人又重新恢复了健康并且开始像往常一样锻炼身体了。