A:a<2
B:a=2
C:a>2
D:a∈R
-How long does it take your father ______ to work every day?
- About half an hour.
One soldier was killed and three others were ____ when their tank was hit by a rocket. (wound)
速度v(m/s)
10
20
30
40
阻力f/N
0.3×102
1.2×102
2.7×102
3.6×102
已知汽车发动机燃油完全燃烧的能量转化为机械能的效率是30%,汽车使用的燃油的热值为4.5×107J/kg,求:
①是根据我国国情对计划生育政策作出的调整和完善
②会直接制约我国经济的发展和人民生活水平的提高
③能调整我国人口结构、缓解老龄化问题
④能解决我国人口基数大的问题,提高我国人口的文化素质