US City Bans Texting while Walking

    Parents usually teach their children how to cross the street safely, by looking both ways for cars. But do they also teach them to put away their cell phones?

    The city of Honolulu, Hawaii wants everyone to learn that lesson____Beginning on October 24, you could be fined from $15 to $99 if you step into a Honolulu street while looking at your phone. Honolulu is the first major U. S. city to ban what is called "distracted (分散注意) walking. " It recently passed a law in a seven to two vote. The law says; “No pedestrian shall cross a street or highway while viewing a mobile electronic device. "____

    The law's creators hope it will lower the number of people hit and killed by cars in the city. Mayor Kirk Caldwell told Reuters news agency, "We hold the unfortunate distinction (区别) of being a major city with more pedestrians being hit in crosswalks, particularly our elders, than almost any other city in the country. "

    The law includes all electronic devices with screens: cell phones, tables, gaming devices, digital cameras and laptop computers____Pedestrians may use such devices in the street to call emergency services and rescue workers, such as firefighters and police officers.

    ____The Governors Highway Safety Association, or GHSA, says pedestrian deaths in the United States increase 25 percent between 2010 and 2015. That trend continued in 2016 with the number of pedestrian deaths rising to almost 6000, 11% higher than in 2015.

    If you still want to text while walking, you could avoid being fined in Honolulu (and be safer, in general) by using a voice-controlled digital(数字的) assistant such as Siri or Google Assistant____

A. The law does permit an exception.

B. Or you could just wait until you are again, safely, off the street.

C. You will be sentenced to prison while using cell phones in the street.

D. Pedestrian deaths have been increasing as the use of cell phones rises.

E. Texting while crossing the street will soon be banned in the city.

F. The law permits people to watch TV while crossing the street.

G. In other words, do not look at a screen when you cross the street or you could be fined.

已知$f\left(x\right)=3\cos \left(x+\frac{3\mathrm{\pi }}{2}\right)+\cos \left(x-\frac{3\mathrm{\pi }}{2}\right)+\sin \left(x+\mathrm{\pi }\right)+a$（a∈R，a为常数）．

（1）若f（x）为奇函数，求a的值；

（2）若x∈R，求f（x）的最小正周期；

（3）若x∈0，$\frac{\mathrm{\pi }}{2}$时，f（x）的最大值为4，求a的值．