who is standing 是个正确的句子那 who are standing为什么不是

"Who is standing" is a correct sentence in which "who" is used as a singular pronoun to refer to a single person. It is asking about the identity of the person who is currently standing.

On the other hand, "Who are standing" is not a complete sentence. The verb "are" is used with plural subjects, so it would be appropriate to use it with a plural pronoun such as "they" or "we." For example, "They are standing" or "We are standing" would be correct sentences.