生物对（）的耐受性范围称为生态幅。
参考答案：生态因子
--- __________ do you chat by QQ with your friend in Shanghai every week?
--- Two hours. I have much homework to do every day.
A．How often
B．How long
C．How far
D．How soon
烟道挡板的作用是（）
A、控制通风量
B、调整炉出口温度
C、控制瓦斯消耗量
