题目

阅读理解 The yearly Academy Awards ceremony was once a private affair. Now, because of television, it is very much a public affair. Hundreds of people gather in Hoolywood to see the Oscars presented to outstanding actors, and others involved（参与） in the motion picture industry. Millions more watch on the television. It all began on May 16, 1929, when 270 men and women sat down to dinner at the Hollywood Roosevelt Hotel. There was no secret about the winners. The names of the winners had been known for months. Janet Gaynor, for example had won as Best Actress. Douglas Fairbanks prese如图：D，C，B三点在地面同一直线上，DC=a，从C，D两点测得A点仰角分别是β，α（α＜β），则A点离地面的高度AB等于 ．