參考答案：

【小題20】C
【小題21】B
【小題22】C

習題解析：

【小題20】聽力原文中提到 It's the Eiffel Tower, designed by Gustave Eiffel and built between 1887 and 1889，指出埃菲爾鐵塔是在 1887 年到 1889 年間建成，因而一共花費了三年的時間，故選 C^=sQ)m&Yq&.R。
【小題21】聽力原文中提到 The tower was built to be the gateway into the 1889 World's Fair in Paris，指出建造埃菲爾鐵塔是為了將其用作 1889 巴黎世界博覽會的大門，故選 BL8[9F2F0[9MR~R。
【小題22】聽力原文中提到 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經(jīng)計劃將埃菲爾鐵塔拆除，但是在到期之后卻將其保留了下來，原因是埃菲爾鐵塔被證明極具通訊價值，故選 C1Z+&UlCKHoo*boEI)。