题目

根据下列事实：①X＋Y2+＝X2+＋Y；②Z＋H2O（冷）＝Z(OH)2＋H2↑；③Z2+氧化性比X2+弱；④由Y、W电极组成的电池，电极反应为W2+＋2e-＝W、Y－2e-＝Y2+，可知X、Y、Z、W的还原性由强到弱的顺序为                       A. X > Z > Y > W               B. Z > W > X > Y    C. Z > Y > X > W               D. Z > X > Y > WA recent study suggested that taking a bottle of water into the exam hall could help students improve their grades. According to the study those who brought drinks, 1. (especial) water, with them when sitting their exams performed up to 10 percent better than those who did not. Comparing their exam results with their normal schoolwork grades, scientists then found that all those who 2. (bring) drinks with them got better grades 3. between 2 and 10 percent. It is unclear 4. drinking water improves exam results. But scientists say having enough water in our bodies and not feeling thirsty could have a 5. （help）effect on our brains. Drinking water may also cut 6. on anxiety, 7. has a bad effect on exam performances. Whatever the explanation, it is obvious that students should try hard to keep enough water in their bodies during exams. So next time, 8. you are going to have a big exam, try 9. (bring) a bottle of water with you. Who knows — it 10. help you pass the exam!