许多人知道美国空军一号是美国总统的专机。事实上,美国总统的专机从1972年起增加到两架。凡是载有美国总统的飞机在空中飞行时的无线电呼号都称为空军一号。但人们 Many people know that the U.S. Air Force One is the U.S. president’s special plane. In fact, the U.S. presidential plane number has been increased to two since 1972. Any radio call sign that carries the U.S. President’s aircraft while in flight is called Air Force One. But people