业业区位理论创始人杜能认为，在一定时期内，“孤立国”各种农产品的市场价格(V)是个常数不变的，并假定各地发展农业生产的条件完全相同，则各地生产同一农产品的成本(E)也是常数不变的。此时，某个经营者能否在单位面积土地上获得最大利润，主要取决于( )。

A．农业生产成本
B．产品市场价格
C．农产品运输费用
D．社会平均利润率

Passage One

If teachers want to find out if their students wrote their own papers, they ______.

A．ask other teachers to read their students’ papers

B．ask their students to list their sources of information

C．can sign up for the Internet service

D．search the Internet and compare papers