I hope everyone can care about ______ the environment and stop ______ things.

A．protecting; wasting

B．protecting; to waste

C．protect; wasting

D．protect; to waste

牙列拥挤可分为（）.

A.遗传性和后天性拥挤

B.单纯拥挤和复杂拥挤

C.替牙列拥挤和恒牙列拥挤

D.前牙拥挤和后牙拥挤

E.青少年拥挤和成人拥挤