题目

This cake is ________ that one. Which of the following is wrong? A. three times the size of            B. three times so big as C. three times bigger than           D. one third as big as 答案：B 解析: 考查比较等级的用法。按照比较级有倍数修饰时应该放在比较级之前的句式来做。如图所示，某装卸工人斜向下推着质量为m的木箱在水平地面上匀速前进。已知木箱与地面间的动摩擦因数为μ，该工人推力与水平面间夹角为α。1.请在图中作出木箱的受力示意图；2.求工人推力的大小。