1.John helps his mother while she cooks.
2.John helps his mother while she is cooking.
3.John helps his mother while she has been cooking.
(A) Are the above sentences correct? I guess first and second sentences may be correct. but I don't know third sentence is correct. and,
(B) I want to know how to use 'while' with tenses.(For an example, when main clause is simple/continuous/perfect/perfect continuous[present,past or future], which tenses must be used with 'while in sub-clause'?)