问题
选择题
A．2∶3
B．1∶3
C．1∶1
D．1∶2
答案
答案：A
据石墨的晶体结构可知：每个碳原子为三个正六边形共用，每个正六边形占有该碳原子的1/3，因此，每个正六边形占有碳原子数为6×
个；晶体中每个C—C键即为每个正六边形的边，每个边为2个正六边形共用，每个正六边形占有该C—C键的
，故每个正六边形占有C—C键数目为6×=3个，选（A）。
搜题请搜索小程序“爱下问搜题”
A．2∶3
B．1∶3
C．1∶1
D．1∶2
答案：A
据石墨的晶体结构可知：每个碳原子为三个正六边形共用，每个正六边形占有该碳原子的1/3，因此，每个正六边形占有碳原子数为6×个；晶体中每个C—C键即为每个正六边形的边，每个边为2个正六边形共用，每个正六边形占有该C—C键的，故每个正六边形占有C—C键数目为6×=3个，选（A）。
| 阅读短文，选择正确答案。 |
| Lucy is a lazy girl. She doesn't study hard, and she doesn't help her mother with the housework, either (也) . "What are you going to be when you grow up (长大), Lucy?" mother asks. "You're too lazy. No job will ever fit (适合) you." " But I know one," says the girl. "I'm going to be Father Christmas (圣诞老人)." "You want to be Father Christmas?" mother is surprised. "But why?" "Because he works only one day in a whole year. " |
| 1. Lucy is a girl. |
[ ] |
| A. lazy B. hard-working C. good |
| 2. Lucy's mother thinks . |
[ ] |
| A. Lucy can find a good job B. Lucy can't find any job C. Lucy isn't too lazy to get a job |
| 3. Lucy wants to be . |
[ ] |
| A. a teacher B. Father Christmas C. a Christmas worker |
| 4. Lucy wants to do that job because . |
[ ] |
| A. that job is interesting B. she likes Father Christmas very much C. she works only one day in a year |