A、One month. B、One week. C、Two weeks. D、Two months. A细节题。短文结尾提到，一次可以借三个物品，可以是三本书或者三个带子，但是物品必须在一个月内归还，可以打电话再续借一个月，可知，在续借以前，读者可以将书

This library is an English language teaching and learning library.[19]Unfortunately our resources are limited and so not everyone can join. Teachers of English, university students and professionals who are in the medical, engineering, and management fields can all join the library. Those from other professions are welcome to apply. But your application will not necessarily be approved. You must fill in a library application form and put it in the box on the librarian’s desk. Because of the high number of applications we receive each week, you must wait one week. Please bring your student or work card to pick up your library cards. Library application forms which are not picked up within two months will be discarded and you will have to reapply.
    You may borrow one video at a time. The video must be returned in one week.[20]If you can’t return it on time, please call. Otherwise your video library card will be cancelled. You may borrow three items at one time.[21]That is three books or three cassettes. Items must be returned within one month. You can telephone the library to renew items for another month.
19. Why can’t the library issue library cards to everyone who applies?
20. What will the library do if a reader fails to renew the video when it is due?
21. For how long can a reader keep the book before he renews it?