类风湿因子的靶抗原是（）
A.IgG
B.IgM
C.IgA
D.变性IgG
E.C3
参考答案：D
Never shall I forget the mountain village ____ I spent my summer holiday last year. [ ]
A. which
B. what
C. where
D. what
桩基承台的混凝土强度等级不宜低于（）。
A.C10
B.C15
C.C20
D.C30
