单选题
Even during the horse and carriage days, traffic in
big cities was often heavy. Police officers had to be stationed full time
directing traffic at busy intersections. The world's first
traffic light came into being before the automobile was in use, and traffic
consisted only of pedestrians, carriages and wagons. On December 10, 1868, the
first traffic lights were installed outside the British Houses of Parliament in
London, by the railway engineer J. P. Knight. They resembled railway signals of
the time, with signaling arms and red and green gas lamps for night use. The gas
lantern was turned with a lever at its base so that the appropriate light faced
traffic. Unfortunately, it exploded on 2 January 1869, injuring the policeman
who was operating it. The modern electric traffic light is an
American invention. As early as 1912 in Salt Lake City, Utah, policeman Lester
Wire invented the first red-green electric traffic lights. On 5 August 1914, the
American Traffic Signal Company installed a traffic signal system. It had two
colors, red and green, and a buzzer, based on the design of James Hoge, to
provide a warning for color changes. The design by James Hoge allowed police and
fire stations to control the signals in case of emergency. The first four-way,
three-color traffic light was created by police officer William Potts in
Detroit, Michigan in 1920. Timers on traffic lights were first
seen in Taipei, China, and then brought to the U.S. after an engineer discovered
its use. Though uncommon in most American urban areas, timers are still used in
some other Western Hemisphere countries. Timers are useful for drivers to plan
if there is enough time to attempt to cross the crossroad before the light turns
red and the amount of time before the light turns green. The
colors of the traffic lights are psychologically associated with the message
they are meant to transmit. Red is classically seen as a color representing
danger or caution. (There are countless phrases and idioms that use "red" as a
message of the bad or unknown--"in the red" and "seeing red.") Green, on the
other hand, is a reassuring color in most cultures--the color of nature and
growth; of harmony, freshness, and fertility. Green has a strong emotional
correspondence with the idea of safety, and was intuitively chosen to guide
pedestrians responsibly through an intersection.
单选题
Before traffic lights were put into place, ______.
A. traffic had begun to show signs of problems
B. cars had already caused some traffic problems
C. traffic congestion was considered out of control