A、Every 6 minutes. B、Every 20 minutes. C、Every 30 minutes. D、Every hour. B短文中提到，定时休息非常重要，最好不要长时间不休息地连续工作。之后又提到，每隔20分钟休息一次是最好的。

(14)Today, I’d like to say something about our memory. Memory ca,n be improved in many ways. In fact, I believe we all have the ability to remember up to six times more than we actually do. A lot of people find that forming a picture of information in the mind is very helpful. For example, if you are trying to remember a telephone number, write it down on a piece of paper. Remembering people’s names is very difficult for a lot of people.(15)I suggest that when you are introduced to someone, you should try to remember his or her first name. It probably won’t make anyone upset if you have to say, "What was your last name again, Sarah?" But Sarah might be upset if you forget her first name. Of course, regular breaks are important and it’s better not to work for long periods of time without taking one.(16)Stopping to rest about every 20 minutes is the best. Finally, take care of your body. Don’t drink or take things like coffee, alcohol or drugs, because they make the mind dull.(17)And don’t forget your vitamins—they are particularly good for memory.
14. What is this passage mainly about?
15. How can we remember a name according to the speaker?
16. How often should we have a break according to the speaker?
17. Why does the speaker suggest we take vitamins?