试述有机磷农药中毒时用解磷定解救的机制。
参考答案：
有机磷农药中毒时可用解磷定解救的原因为：有机磷农药是胆碱酯酶抑制药，中毒时乙酰胆碱不被分解而大量蓄积，产生全身中毒症状，常用解磷定等药解救。因为解磷定是胆碱酯酶复活剂，能将中毒酶的磷酰基解脱下来，使胆碱酯酶重新恢复活性，发挥水解乙酰胆碱的作用。此外，解磷定也能直接与体内游离的有机磷酸酯类结合，使之成为无毒的化合物排出体外。
| 阅读理解 |
| The final exam comes in June. When the exam ends(结束) , the summer vacation begins. Boys and girls have about two months to relax. The summer vacation is the best part (部分) of year for most children. The weather is usually fine. They can swim, go to summer camp or visit other places with their parents. Of course, the beaches are good places for relaxing. Some children are lucky(幸运的) to live near the sea(大海). They can enjoy the sea anytime(任何时候). But for the children far(远的) from the sea, they go to the beaches for one or two weeks with their parents. Why do children like spending their summer vacation on the beaches? It is because they like the sand(沙) , the sun, the cool wind and the sea water. There are lots of new things to see, nice things to eat, and exciting things to do. |
| 1. School children usually have exams . |
| A. in June B. after June C. before June |
| 2. The summer vacation is about . |
| A. two weeks B. two months C. three months |
| 3. Why do children like summer vacation? |
| A. Because the weather is fine. B. Because it is long. C. Because the weather is fine and they can have lots of activities. |
| 4. Children near the beach can enjoy the sea____ |
| A . anytime they enjoy it B. for one or two weeks C. for two months |
| 5. Which of the following is not right? |
| A. Children like going to the beaches only because they can see lots of new things. B. Children like summer vacation best. C. Children can swim and enjoy the sand, wind, and water on the beaches. |