21．What's the main function of the Adler Planetarium Chicago?

　　A．Displaying the models of the Solar System.

　　B．Selling ancient astronomical instruments.

　　C．Offering a passageway to explore the universe.

　　D．Giving 10­minute lessons to visitors.

　　解析：选C　细节理解题。根据第一段的"From huge models ...provide a passageway for you to explore the universe"可知，阿德勒天文馆给游客提供了探索太空的途径，故选C项。

　　22．What can visitors learn in the StarRider Theater?

　　A．The history of the Adler Planetarium Chicago.

　　B．The wonder of the interactive adventures.

　　C．The complicated Digistar 3TM technology.

　　D．The movement of the stars in the night sky.

　　解析：选D　细节理解题。依据第二段的最后两句可知，游客在这里能了解到星星在夜空中的运动，因此选D。

　　23．If you want to try the Doane Observatory, you'd better ________.

　　A．drive your private car

　　B．consider weather conditions

　　C．buy a telescope in advance

　　D．join the Adler's summer camp

　　解析：选B　细节理解题。依据"Don't Miss the Doane Observatory: when weather permits ..."可知，选B。

　　24．How much will a couple and two kids at least spend to visit the Adler?

　　A．＄37.　　　　　　　　　 B．＄63.

　　C．＄72. D．＄100.

　　解析：选B　数字计算题。依据Ticket Price部分可知，成年人每人28美元，儿童22美元，一对夫妇和两个孩子则是(28×2)＋(22×2)＝100，如果在网上订，则会在总价的基础上优惠37%，即至少为63美元，故选B。

　　B

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