2*2*72000000/300000000（光速）=0.96S 因为,信号传过去需2*72000000/300000000（光速）=0.48S,他的回话2*72000000/300000000（光速）=0.48S后传回,所以距你说话已过2*2*72000000/300000000（光速）=0.96S