一道初中英语题不算太难！

let's= let us
这是最常见的祈使句之一

就语法上而言：
Let's not play tennis with Peter.是成立的！

但从实际运用上，人们倾向于使用：
Do not do sth 也就是 Don't do sth.
既是 Don't play tennis with Peter.(命令语气)
或是Please not play tennis with Peter.（请求语气）

Let's not play tennis with Peter.

Let's not play tennis with Peter.

Let is not play tennis with peter.

Let's not play tennis with Peter.

Let's play tennis without Peter
Let's don't play tennis with Peter