参考答案：

【小题20】C
【小题21】B
【小题22】C

习题解析：

【小题20】听力原文中提到 It's the Eiffel Tower, designed by Gustave Eiffel and built between 1887 and 1889，指出埃菲尔铁塔是在 1887 年到 1889 年间建成，因而一共花费了三年的时间，故选 ClyBTpU82cIU。
【小题21】听力原文中提到 The tower was built to be the gateway into the 1889 World's Fair in Paris，指出建造埃菲尔铁塔是为了将其用作 1889 巴黎世界博览会的大门，故选 BY,&9Qylju*!E,8o6tJeP。
【小题22】听力原文中提到 The City of Paris had planned to tear it down but as the tower proved valuable for communication purposes, it was allowed to remain after the permit expired.由此可知巴黎市政府曾经计划将埃菲尔铁塔拆除，但是在到期之后却将其保留了下来，原因是埃菲尔铁塔被证明极具通讯价值，故选 CPompwoC-,BT;o!NW3&8[。