---Must I learn the new words in heart today?---No, you _______. You ______ do it tomorrow. 

A．needn’t; may

B．mustn’t; must

C．mustn’t; may

D．needn’t; mustn’t

For centuries animals have been used as surrogates for people in experiments to assess the effects of therapeutic and other agents that may be later used for humans.

A. which may later be used fr humans
B. that may be later used in humans
C. which might later be used for humans
D. that might later be used in humans