单项选择题
A．they found it no use doing so B．they liked staying at home C．there was no modern transportation D．they were forbidden to go to other countries
A．it is interesting B．it is cheaper than to go in any other way C．it can cross the wide oceans D．it takes less time
A．it can bring us more knowledge B．it can make us rich C．they have too much money D．it is a good idea