-- Who taught you to dance so ________? --- Mr. Yang ____________. A. well, did B.good, did C. well, do D. good, do 答案:A14.先后任意地抛一枚质地均匀的正方体骰子两次,所得点分别记为a和b,则函数f(x)=$\frac{1}{3}$x3+$\frac{1}{2}$ax2+bx存在极值的概率为( )A.$\frac{13}{36}$B.$\frac{17}{36}$C.$\frac{19}{36}$D.$\frac{23}{36}$