They shouted when they saw the famous singer____

问题描述:

They shouted when they saw the famous singer____
老师说是appear 不用appering、为什么?如果改成performing可以不
貌似有see sb doing、、

see sb. doing sth. 是指看见某人正在做某事
see sb. do sth.是指看见某人做某事(指整个过程)