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I'm not sure that I can make it much easier for you, but--
Be (the copula) and other linking verbs have the SVC structure, where C is a noun or an adjective:He is a man.He is handsome.Nouns can be single-word nouns, noun phrases or noun clauses, and they all work into an SVC sentence in the same way:They are dogs. (N)
They are big black dogs with sharp teeth. (N phrase)
They are what you don't want to meet alone on a dark night. (N clause)
The problem with meeting them is that you might be their dinner. (ditto)
Does that help any?