What does the phrase “waving a red flag” mean?

How are introductions conducted in English?

Explain the functions nonverbal messages perform in human communication.

你对他期望过高了。干这活他还是新手呢。

天网恢恢，疏而不漏。

饭菜不好，请大家随便吃。

Please return the book to me as soon as you’ve read it.

—Hasn’t he approved your plan?

—Yes, he has.

You’re invited to come to my house. (用敬语翻译)

What does the phrase “waving a red flag” mean?

What is body language?