试述城市轨道交通信号的颜色及其表示意义。

A. 干粉
B. 泡沫
C. 二氧化碳

A. 进行测量时，应先按下电源按钮，同时按下检流计P按钮，
B. 使用前，应首先将仪器置于水平位置，把检流计锁扣打开，观察指针是否准确地指在零刻度上
C. 测量完毕后，应断开检流计P按钮，再断开电源按钮
D. 用电桥测量电阻时，均不许带电测试

A. "Indirectly， relativity paved the way for a new relativism in morality， art and politics，"Isaacson wrote in an essay explaining Time"s choices.
B. How he thought of the relativity theory influenced the general public"s view about Albert Einstein.
C. "Clearly， no scientist better represents those advances than Albert Einstein."
D. Roosevelt heeded the advice and formed the "Manhattan Project" that secretly developed the first atomic weapon.
E. In his early years， Einstein did not show the promise of what he was to become.
F. In his "Special Theory of Relativity，" Einstein described how the only constant in the universe is the speed of light.