函数y=（k+1）xk2是正比例函数，则常数k的值为______．
k+1≠0，k2=1，
∴k=1．
故填1．
Don’t worry! Philip is quite used to in such busy streets as this.
A．drive
B．be driving
C．have driven
D．driving
总成本函数（Total cost function）
