题型：问答题 论述题 完形填空。 In the past all letters were sent by train or ship. Now most letters are __1__ sent by train or ship, but some are sent by air. You send a letter __2__ so that your friend may receive it sooner. A letter __3__ about twelve days to go from England to India by train or by ship. A letter can get to India by air __4__ five days now, but __5__ the time may be made shorter. __6__ people were afraid to send letters by air. They thought that the plane might fall and their friends might not receive the letter. So they sent two letters: one letter by air and __7__ by train or ship. They wanted to __8__ that the letters would be received. Planes are now almost as safe __9__ trains or ships. __10__ letters are sent by air,( )1. A. still ( )2. A. by ship ( )3. A. takes ( )4. A. in ( )5. A. by then ( )6. A. At last ( )7. A. other ( )8. A. know ( )9. A. as ( )10. A. More or less B. just B. by air B. take B. on B. soon B. At times B. the others B. see B. the same as B. Much and much C. already C. by train C. took C. after C. quickly C. At first C. the other C. hear C. than C. More and more D. yet D. by bus D. is taken D. during D. fast D. So far D. another D. make sure D. like D. Many and many 查看答案
题型：问答题 论述题 金属元素R的最高价氧化物的化学式为RmOn，则R元素的最高化合价为______；R元素（核电荷数小于18）原子最外电子层的电子数是______；若RmOn的相对分子质量为Mr，则R元素的相对原子质量为．______． 查看答案
题型：问答题 论述题 1211、1301灭火剂具有优良的灭火性能，但是释放后的( )与大气层的臭氧会发生反应，致使臭氧层出现空洞，使生存环境恶化，所以逐渐被淘汰。A．C02B．COC．卤代烷灭火剂D．惰性气体 查看答案
题型：问答题 论述题 公共预算决策成本—效益分析的步骤有（）A.计算各项目或方案的效益和成本B.计算各项目或方案的效益和成本的比率C.确定各项目或方案的优劣次序D.进行各项目或方案的选择和策E.计算预算资金的机会成本 查看答案