你好，1. The teacher called on Sarah to answer the question.
2. The boss called on John to present his project at the meeting.
3. The police officer called on the witness to testify in court.
4. The principal called on the students to behave well during the school assembly.
5. The coach called on the player to step up and take the penalty shot.
call on拜访，访问
call on后接表示人的名词或代词
I called on the doctor yesterday.
我昨天去拜访了医生.
call sb up释义：
征召；打电话
例句：
We can not only send messages, call sb. up, but also can play games, and some even surf the internet.
但是，现在手机又那么多功能，不只局限于打电话发短信，还可以玩游戏，甚至上网。
call up sb释义：
打电话
例句：
We can not only send messages, call sb. up, but also can play games, and some even surf the internet.
但是，现在手机又那么多功能，不只局限于打电话发短信，还可以玩游戏，甚至上网。
当sb是不定代词的时候，只能是call sb up, 例如，call her up,call him up... 当sb是人名或指定的某人时候，比如 call Tom up, call up Tom, call mom up, call up mom...两种表达都是对的，只有sb是不定代词时候，只能为call sb up. 拓展资料： call sb.意同 ring sb. up/telephone sb.表示给某人打电话。
而call sb. at 相当于 visit sb.表示登门拜访某人的意思。