能编码HIV的gP120包膜蛋白基因是
A.HIV的gag基因
B.HIV的env基因
C.HW的LTR基因
D.HIV的tat基因
E.HIV的pol基因
参考答案:B
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的矩估计量;
He's worked here _______ the factory opened. [ ]
A. before
B. since
C. after
D. for