已知A={1，3，5，7}，B={2，3，4，5}，则集合A∩B的子集的个数是（　　）

A．4

B．6

C．8

D．9

—Your colleague's spoken English is quite good, Amy.

— No wonder, as she              in the USA for two years.                  [ ]

A. worked

B. has been working

C. had worked

D. has worked