对眼睛刺激作用最强的是
A．臭氧B．过氧乙酰硝酸酯C．铅D．甲醛E．苯并芘
参考答案：D
Linda often _____ her homework in the evening, but this evening she _____ TV. [ ]
A. does; watches
B. is doing; watches
C. does; is watching
D. is doing; is watching
简述物流系统的特征
