My father was watching me --when someone knocked at the door

My father was watching me __when someone knocked at the door 1 分钟前 甜幂星月 | 浏览次数：7次A plays the pianoB playing pianoC playing the piano D play piano答：C译：我父亲正在看我弹钢琴,就在这时有人敲门。析：本题考非谓语动词作宾补用冠词用法。演奏乐器,一般用定冠词the,play the piano,排除BDwatch sb。doing sth。排除A。评：出题者过于谨慎。如果楼主没有抄错的话,A项应该是play the piano才对。否则第二次排除就太简单了。因为plays the piano是谓语动词显然不对,不能说：watch me plays the piano的。如果是play the piano,无to不定式,则要思考,为什么这里不能用watch sb。do sth。要从句意及逻辑上来判断。watch sb。doing sth。是看某人在做某事。watch sb。do sth。是看某人做了某事。