Shanghai has become a (n) ________ of the world’s attention with the 2010 Expo being held at the moment.

A．attraction

B．focus

C．thrill

D．excitement

应用哪种单抗组合在流式细胞仪上计数可检测外周血中B淋巴细胞总数以及B1细胞和B2细胞（）。

A.CD19和CD20

B.CD10和CD19

C.CD5和CD10

D.CD5和CD19

E.CD10和CD20