单项选择题
A．at the beginning of the nineteenth century B．in the middle of the nineteenth century C．more than two hundred years ago D．when people first sent letters and postcards.
A．the moon is 240 kilometer far away B．we don't know where it is C．it can't fly without air D．there is no air on the moon
A．in a few months B．in a few days C．in six months D．in one day