题目

The president spoke at the business meeting for nearly an hour without ______ his notes.        A. bringing up              B. referring to        C. looking for               D. trying on 答案：B 解析: 略人们常用三角形的（　　）性生产自行车大梁，运用平行四边形的（　　）性应用电动大门．A.稳定性 B.易变形 C.平衡性