巴西的铁、哥伦比亚的（），储量均居世界前列。
A.石油
B.银
C.绿宝石
D.锡
参考答案：C
The teapot ______ for keeping tea hot after it ______. [ ]
A. was using; was made
B. was used; was made
C. using; is making
D. uses; makes
什么是诱导性技术进步理论？
