—How often do I need to feed the birds?

—They _______ food every day, or they will be hungry.[ ]

A. must give

B. mustn't give

C. must be given

D. mustn't be given

＿＿＿＿＿＿ for the free tickets, I would not have gone to the films so often.

A．If it is not

B．Where it not

C．Had it not been

D．If they were not