A. consumer’s wants and needs B. customer cost C. customer convenience D. customer communication
Apple B. SUN C. Motorol DE
A. 隔绝进回风,不允许风流通过; B. 隔绝进回风,可以让风流通过; C. 控制进回风,防止瓦斯超限; D. 控制进回风,防止瓦斯溢出。