题目

已知某粒子AzRn+ ， 则元素R原子的电子数为（ ） A . Z B . A-Z C . A-Z+n D . A-Z-n 答案：AThe weather is getting hotter. You are thirsty playing basketball or riding home from school. A cold drink may be just the thing. But be careful what you are drinking. Something that looks cool may not be good for your health. There are plenty of "energy drinks" on the market. Most of them have beautiful colors and cool names. The lists on them tell you they are helpful to your health. Sounds great!   But after a careful check you may find that most energy drinks have lots of caffeine (咖啡因) in them. These drinks are especially aimed at young people, students, busy people and sports players. Makers sometimes say their drinks make you better at sports and can keep you awake. But be careful not to drink too much. Caffeine makes your heart（心脏）beat fast. Because of this, the International Olympic Committee has limited(限制) its use. Caffeine in most energy drinks is at least as strong as that in a cup of coffee or tea. Possible health dangers have something to do with energy drinks. Just one box of energy drink can make you nervous, have difficulty sleeping and can even cause heart problems. Scientists say that teenagers should be discouraged from taking drinks with a lot of caffeine in them. 1.The main reason for people not to drink too much energy drinks is that they may cause      . A．heart problems                         B．nervousness C．sleeping difficulty                       D．possible health dangers 2.The underlined word "discouraged" can be replaced(替换) with "________". A．encouraged        B．stopped           C．helped           D．disliked 3.From the passage we can know that _________. A．advertisements are important in getting people to buy energy drinks B．energy drinks are helpful to teenagers' study C．sports players need to drink a lot of energy drinks D．energy drinks are especially aimed at teenagers