A、How primitive people used flags. B、What the ancient means of communication was. C、Why the torch towers were built. D、How the G

W: There is a direct flight at 10 o’clock or a flight at 2 this afternoon that stops over in San Francisco.
M: I think I’d rather have the earlier one so I can go to work tomorrow.
Q: What relationship do these people have?

M: People first sent signals by flags, some archaeologists observed.
W: No. I think they exchanged news by smoke, hence the torch towers on the Great Wall.
Q: What are they discussing?