In my English book I came upon this sentence:
It may sound (strange/strangely).

Well, I chose strange of course, but my English teacher couldn't explain me why it has to be strange instead of strangely.
It says something about the verb (to sound) and thus has to be an adverb.

Can someone explain me why it has to be strange?
The verb sound is a copula, which is followed by a predicate noun or adjective, describing the subject. The adjective form is required.
It (the story) is strange. It is a strange story. It seems strange to me. It sounds strange. It even looks strange.

Compare with an adverb of manner:
He walked strangely, as if he were drunk.

He is not a strange person, but he is walking in a strange manner. The adverb is required.
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sound is a sensory verb ,so I think it can be followed by a adj, for example, It tastes good ,or it looks nice
Thank you for your answering quickly. After reading your posts it sounds very logical.