设X1，X2…，Xn是来自总体X的简单随机样本，且总体X的密度函数为
求θ的极大似然估计量．
参考答案：
[*]
Though most people know that smoking __________ the risk of cancer, it is still hard for them to give it
up. [ ]
A. multiplies
B. adds
C. combines
D. gains
三一专用生物肥生物固氮效应是怎么回事？
