世界上国家最多的大洲是[ ]
A、非洲
B、亚洲
C、欧洲
D、大洋洲
答案：A
试述成本变化对商品供给变化的作用过程。
As _____ announced in today's papers, the Shanghai Export Commoditiser Fair is also open on Sunday.
A．being
B．is
C．to be
D．been
