题目

16、老年人头发变白的直接原因是头发基部细胞内（   ） A．物质转运加速        B．新陈代谢变缓 C．呼吸速率加快        D．与黑色素合成相关的酶活性降低 答案：DHe is a bit ill, but he goes to school _____ at home. [     ]A. insteadB. instead ofC. instead of stayD. instead of staying