I have three questions to ask someone.Come in for help me.

19. Don't let your brothers ____seen____ the present.
(A) to see
(B) seeing
(C) seen
(D) see

why the answer is seen?
i don't understand.

Will you be ____so____ kind as to help me with this heavy box?
(A) as
(B) so
(C) very
(D) enough


why the answer isn't very?
i don't understand.


18. - What instructions did your boss give you? - He required that Bill _attend_______ the meeting.
(A) would attend
(B) attends
(C) attended
(D) attend

why the answer isn't attends?
i don't understand.