You can have a good view of Nanjing at the top of Zijin Mountain ______ a clear day.
A:at
B:on
C:in
D:for
2011年全世界的人口为7000000000人,这里的7000000000改写成用“亿” 作单位的数。
如图,抛物线y=﹣ 23 x2+bx+c经过A(﹣1,0),B(0,2)两点,将△OAB绕点B逆时针旋转90°后得到△O′A′B′,点A落到点A′的位置.
In some cities, the junior pupils look forward to having ______ time to relax and ______ homework to do.
构成原子核的粒子一定有( )