The teacher saw the students ----(play) on the playground at

The teacher saw the students 【playing】 on the playground at 5 pm yesterday。see sb do sth 省略to的不定式,即动词原形做宾补,强调【动作全过程】see sb doing sth v-ing做宾补,强调【动作正在进行】see sb/sth done 过去分词做宾补,强调【宾语与该动作是被动关系】这里,突出动作正在进行,因此用playing。再如：The managers would like to 【see the plan carried out】when they come back。The lost boy were last seen playing on the beach。The witness 【 saw the defendant come over and enter】 that house through the window。祝你开心如意!