"Please stand" 用英语说是 "Please stand up"。
"Please sit" 用英语说是 "Please be seated"。
“Stand up” 与 “sit down” 这两个短语都是英语中常用的语言，用于礼仪场合或者组织会议，表达敬意或者纪律性要求。
例句：
Please stand up for the national anthem. (请站起来唱国歌)
Could you please be seated? We're about to begin the meeting. (请坐下，我们将开始会议)
The teacher asked the students to stand up. (老师要求学生起立)
The judge asked the defendant to stand up. (法官要求被告起立)
The audience was asked to be seated before the performance began. (在表演开始之前，观众被要求坐下)