A、In art. B、In geometry. C、In engineering. D、In circus performance. A四个选项均是“In+名词”构成的介词短语，art，geometry和engineering属于学科领域，因此推测该题可

You probably know what a mobile is, but the mobile I’m talking about is a delicate object of decoration hanging from the ceiling and moving gently with every breath. It delights both children and adults. Now, do you know who invented the mobile? This lovely creation was the work of an American artist named Alexander Calder. Calder became interested in making things when he was a child. And even then he often used wire in his constructions. When he went to college, he studied engineering rather than art. But he quickly realized that art was his real passion. He also loved the circus, and many of his early artworks were small circus figures made with wire. In about 1930, Calder turned from realistic wire figures to abstract ones. He began constructing objects that have circles, squares and other geometric shapes. To get the shapes to move, he used small motors. Then he went one step beyond these early mobiles. He got the shapes in his constructions to move by themselves. A mobile may look simple as it shifts in the wind, but it requires careful construction to work properly. Calder used his engineering knowledge to create his first mobiles. Often these consisted of small pieces of brightly printed metal strung by wire to a thicker base wire. Calder learnt how to find the precise point to connect each wire so that all the pieces will sway in harmony. In doing so, he created an art form for people all over the world to copy and enjoy.
16. What does the speaker say about a mobile?
17. What do we learn about many of Alexander Calder’s early artworks?
18. Where does Alexander Calder’s real passion lie?