— Did you happen to see _______ black and _______ white cat?

— Are they missing? I told you to take care of them.

A．a; 不填

B．the; 不填

C．the; the

D．a; the

黄土高原农作物的熟制主要是：[ ]

A．一年三熟

B．一年一熟

C．随时播种，四季都有收获

D．一年两熟或两年三熟