《When was it invented?》SectionD PPT
《When was it invented?》SectionD PPT第4页

GPS is like a man-made star. We can use it at any time, in any place and in any weather to find out our position. The early explorers used the stars as landmarks to know where they were and in which direction they were going. This method worked well at night as long as the weather was good. But it didn’t work so well during the rest of the time.

Let’s use the GPS.

n.探险者, 勘探者