三种检测HIV抗体的基本筛选方法是（）
A.酶联免疫吸附试验（ELISA.
B.颗粒凝集试验
C.特异性快速试验
D.PC.R
参考答案：A, B, C
He often helps his classmates their English. [ ]
A. to
B. with
C. on
D. in
组成为C3H6FCl的卤代烃，可能存在的同分异构体有 [ ]
A.3种
B.4种
C.5种
D.6种
