是hear sb to do sth 还是hear sb doing sth
问题描述：
是hear sb to do sth 还是hear sb doing sth
答
hear to do 表示动作的全过程；hear doing表示动作正在进行.
如：1、She heard the telephone ringing.她听见电话铃正在响.
2、A pen was heard to drop. 我听见一支笔掉落.