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what

As a subject what may be either singular or plural, though singular is more common, especially with linking verbs.

If what clearly stands for plural quantity, use a plural verb. When what is the subject of a clause that is itself the subject of the sentence, maintain the same number throughout.

 
Britain relinquished its claim to what is now Oregon and Washington. (In this sentence “what” means “the area.”)
What remains of the railway is scraps of rusty iron. (“What” means “the only thing.”)
What appear to be six different images hang on the wall. (“What” means “the things.”)
He had to deal with what are described as manufacturing imperfections. (“What” means “the things.”)