直线y=3x+1的斜率是（ ）
A．1
B．2
C．3
D．4
因为直线y=3x+1是直线的斜截式方程，所以直线的斜率是3．
故选C．
— How come you are late for such an important meeting?
— ____ But I was stuck in a traffic jam. [ ]
A. I'm sorry.
B. Pardon?
C. Take it easy
D. Nothing serious
计算题：某焚硫炉外径d=5m，长L=15m，外壁温度是50℃，炉壁外侧对大气的综合对流传热系数为20W.m-2.K-1，周围大气温度为25℃，该焚硫炉的热损失是多少？
