Consider a wh-question (in english language) such as "Who closed the door?". Personally, I can determine that an answer will look like "NP closed the door.", where NP would be a noun phrase. Another example is "What is John looking at?". I can determine that the answer will look like "John is looking at NP".
Is there a proper way to determine structure of such answers (preferably computational or algorithmical)? Are there any specifications for what a proper english question must look like in terms of POS-tags?
P.S. There is no need for a comprehensive answer, which would cover all possible wh- questions. I also would be grateful for help with any special case:
For example, I assume (correct me if I am wrong) that a question of form
(SBARQ (WHNP (WP Who)) (SQ (VP)) (. ?))
Must have an answer of form
(S (NP) (VP) (. .))