一笔回购交易涉及两个交易主体、（）交易契约行为。
A．一次
B．三次
C．四次
D．二次
参考答案：D
As the world’s population continues to grow，the ________ of food becomes more and more of a concern. (2013·浙江，4)
A．worth
B．supply
C．package
D．list
如何戴无菌手套？
