下列各物质中,分子间只存在色散力的是( )。
A.HBr B.NH3 C.H2O D.CO2
参考答案:D
The Internet is increasingly accessible at school and at home. _____many parents and teachers are sometimes not as prepared as we should be to warn children about Internet threats.
A.Actually
B.Generally
C.Surprisingly
D.Unfortunately
中国政府把控制人口数量增长,提高人口素质作为一项()。