确定道路最小纵坡的依据是（）。
A.汽车动力性能
B.道路等级
C.自然因素
D.排水要求
参考答案：D
函数f（x）=ax2+lnx+1在[e，+∞）上是减函数，则实数a的取值范围是______．
The traffic is heavy these days, I ______ arrive a bit late, so could you save me a place? [ ]
A. can
B. must
C. need
D. might
