You never see him, but they're with you every time you fly. They record where you are going, how fast you're traveling and whether everything on your airplane is functioning normally. Their ability to withstand almost any disaster makes them seem like something out of a comic book. They're known as the black box.

  When planes fall from the sky, as a Yemeni airliner did on its way to Comoros Islands in the India ocean June 30, 2009, the black box is the best bet for identifying what went wrong. So when a French submarine (潜水艇) detected the device's homing signal five days later, the discovery marked a huge step toward determining the cause of a tragedy in which 152 passengers were killed.

  In 1958, Australian scientist David Warren developed a flight-memory recorder that would track basic information like altitude and direction. That was the first mode for a black box, which became a requirement on all U.S. commercial flights by 1960. Early models often failed to withstand crashes, however, so in 1965 the device was completely redesigned and moved to the back of the plane – the area least subject to impact – from its original position in the landing wells (起落架舱). The same year, the Federal Aviation Authority required that the boxes, which were never actually black, be painted orange or yellow to aid visibility.

  Modern airplanes have two black boxes: a voice recorder, which tracks pilots' conversations, and a flight-data recorder, which monitors fuel levels, engine noises and other operating functions that help investigators reconstruct the aircraft's final moments. Placed in an insulated (隔绝的) case and surrounded by a quarter-inch-thick panels of stainless steel, the boxes can resist massive force and temperatures up to 2,000℉. When submerged, they're also able to emit signals from depths of 20,000 ft. Experts believe the boxes from Air France Flight 447, which crashed near Brazil on June 1,2009, are in water nearly that deep, but statistics say they're still likely to turn up. In the approximately 20 deep-sea crashes over the past 30 years, only one plane's black boxes were never recovered.

What does the author say about the black box?

A. It ensures the normal functioning of an airplane.

B. The idea for its design comes from a comic book.

C. Its ability to resist disasters is incredible.

D. It is an indispensable device on an airplane.

What information could be found from the black box on the Yemeni airliner?

A. Data for analyzing the cause of the crash.

B. The total number of passengers on board.

C. The scene of the crash and extent of the damage.

D. Homing signals sent by the pilot before the crash.

Why was the black box redesigned in 1965?

A. New materials became available by that time.

B. Too much space was needed for its installation.

C. The early models often got damaged in the crash.

D. The early models didn't provide the needed data.

Why did the Federal Aviation Authority require the black boxes be painted orange or yellow?

A. To distinguish them from the colour of the plane.

B. To caution people to handle them with care.

C. To make them easily identifiable.

D. To conform to international standards.

What do we know about the black boxes from Air France Flight 447?

A. There is still a good chance of their being recovered.

B. There is an urgent need for them to be reconstructed.

C. They have stopped sending homing signals.

D. They were destroyed somewhere near Brazil.