在下列交通标志中,既是轴对称图形,又是中心对称图形的是( )
A:
B:
C:
D:
—My brother and I will go to the library tomorrow.— . Shall we go together?
如图所示,当带正电的绝缘空腔导体A的内部通过导线与验电器的小球B连接时,问验电器是否带电?
An ant was drinking by a small river when it fell in.It made ______ efforts to reach the side,but made no progress at all.