Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.

The first traffic signal was invented by a railway signaling engineer. It was installed outside the Houses of Parliament in 1868. It ______(31) like any railway signal of the time, and was operated by gas. However, it exploded and killed a policeman, and the accident ______(32) further development until cars became common.

Modern traffic lights are an American invention. Red-green ______(33) were installed in Cleveland in 1914. Three-colour signals, operated by hand from a tower in the ______(34) of the street, were installed in New York in 1918. The ______(35) lights of this type to appear in Britain were in London, on the junction between St. James’ Street and Piccadilly, in 1925. Automatic signals were installed a year later.