下图为某地理事象过程示意图，若（   ）

若$f\left(x\right)=3\sin \left(2x+\phi \right)$＋$a$，对任意实数$x$都有$f\left(\frac{\mathrm{\pi }}{3}+x\right)=f\left(\frac{\mathrm{\pi }}{3}-x\right)$且$f\left(\frac{\mathrm{\pi }}{3}\right)=-4$，则实数$a$的值等于（ 　 ）

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C

　　“Travelling by subway (地铁) is much faster. It not only takes me a few minutes to get to my office, but also I don't worry about traffic jam.” a passenger says. A lot of people like taking the subway. It is a kind of popular way and more convenient in our daily life. It has three advantages (优点). First, it's fast. The subway can run about 80 kilometres in an hour. It's much faster than riding a bike or taking a bus. Second, it's accurate. It can help you get somewhere on time. Don't worry about the weather. It can arrive on time even if it is raining or snowing. During rush hour (交通高峰期), there is a subway every five minutes. You can't wait too long. Finally, it is comfortable. It is very comfortable for passengers to take the subway. You can find place to sit or stand here and there. They don't feel cold in winter or hot in summer because of the air-conditioners (空调). It can carry many people. I think most of people all like it. You will have a good time to take the subway.

已知光的速度是每秒行走300 000km，经历一年时间光行走____km，已知光从银河系的一边射出，当光到达对边时所经历的时间是70 000年，则银河系的范围是____km．