关节腔积液进行微生物学检查，应采用第几管的标本（）。

A.第一管

B.第二管

C.第三管

D.第四管

E.第五管

Xavier, Y vonne, and Zelda each try independently to solve a problem. If their individual probabilities for success are  and , respectively, what is the probability that Xavier and Yvonne, but not Zelda, will solve the problem ？（）

A.A

B.B

C.C

D.D

E.E