问题补充：
There are five pairs, but Im at a loss which to buy.
A. to be chosen
B. to choose from
C. to choose
D. for choosing
答案：
A. to be chosen
B. to choose from
C. to choose
D. for choosing
解析：
此题容易误选C，其实应选B。choose表示“选择”，其实是指“选择出来”(pick out)，而不是指“从……选择”，要表示后者的意思，要用choose from，有时也用choose among。同样地，下面两例中的介词from也不可省略：
Here are some books for you to choose from.这些书可供你选择。
There are too many cakes to choose from.蛋糕太多了，不知要选哪个好。
比较：He didn know what to choose.他不知道选什么。
He didn know what to choose from.他不知道从哪儿去选。
