题目

 Was it on a lonely island ______ he was saved one month after the boat went down?   A. where              B. that                      C. which                  D. what 答案：B20．已知某正态分布的概率密度函数为f（x）=$\frac{1}{\sqrt{2π}}$e${\;}^{-\frac{（x-1）^{2}}{2}}$，x∈R，则函数f（x）的极值点为x=1，x落在区间（2，3]内的概率为0.1359．