You are trying to decide whether to purchase the latest Harry Potter book online or borrow it from the library. There is no charge for borrowing a book from the library, but going to the library takes more time than ordering a book online. Regardless of how you get the book, its benefit to you is the same. If the cost of buying the book online is $13, then you should:

A.buy the book online because it takes less time.

B.borrow the book from the library because you can get it from the library for free.

C.borrow the book from the library if the cost of doing so (in terms of the extra time it takes) is greater than $13.

D.borrow the book from the library if the cost of doing so (in terms of the extra time it takes) is less than $13.

正确答案：borrow the book from the library if the cost of doing so (in terms of the extra time it takes) is less than $13.