在Visual FoxPro中，其扩展名为.mem的文件是______。

A．备注文件

B．内存变量文件

C．报表格式文件

D．屏幕格式文件

An investor gathers the following information about three U. S. Treasury annual coupon bonds:

Given the above information, how can the investor generate an arbitrage profit()

A. Purchase bond 1 while selling bonds 2 and 3.

B. Purchase bonds 2 and 3 and selling bond 1.

C. Purchase bonds 1 and 3 while selling bond 2.