2008年9月国家有关部门检出了以三鹿婴幼儿奶粉为首的一批奶制品中掺和的三聚氰胺，并立即对全国的这些奶制品加以封存或销毁。三聚氰胺本是一种优良的化工原料，主要用来制涂料和黏合剂，它的相对分子质量介于100与200之间，碳的质量分数为28.57%，碳、氢的质量比为6:1，其余为氮。则三聚氰胺的分子式为
A．(CH2N2)n
B．C3H4ON5
C．C3H6N6
D．C4H4N5
答案：C
又碳、氢的质量比为6:1，即N（C）：N（H）=1：2
若N（C）=3，得N（H）=6；若N（C）=4，得N（H）=8；
即可得正确答案为C；
| 完形填空。 | |||
| Villagers are more healthy than people who live in towns. Orie reason for this is that country air is fresher than the air in 1 . The villager breathes fresh clean air all day in the fields, but the air the townsman 2 is always full of smoke and dust. We can't live without air. If we are stopped from breathing 3 for five minutes, we will die. Bad air means bad health and certain kinds of 4 , which may kill us in the end, 5 they may not kill us at once. We all 6 what unpleasant feelings we get if we stay a long time in a shut, crowded room. After a time, we begin to feel very 7 , and can hardly keep our eyes open. Then our heads begin to ache, and the longer we stay, the worse we feel. How nice it is when we get 8 into the fresh air outside. We must, therefore, keep our windows open, so that the 9 in our houses is always fresh, and we should breathe as much as we can in the open air. For people who breathe 10 air for a long time often get very ill and die of lung diseases. | |||
| ( )1. A. factories ( )2. A. breathes ( )3. A. still ( )4. A. experience ( )5. A.so ( )6. A.imagirle ( )7. A. sleepy ( )8. A. up ( )9. A. air ( )10 . A. humid | B. cities B. eats B. as B. stress B.though B.know B.lonely B. down B. environment B. clean | C. streets C. takes C. even C. death C. since C. fear C. energetic C. out C. furniture C. open | D. fields D. smells D. except D. illness D. also D. expect D. exhausted D. off D. wind D. bad |