He looked around and caught a man _______ his hand into the pock

He looked around and caught a man _______ his hand into the pocket of a passenger.
A、put
B、to be putting
C、to put
D、putting
【正确答案】：D
【题目解析】：catch sb doing sth 意为“碰上某人在做某事”或“逮住某做某事”