题目

Not only I but also Tom and Jack _____ interested in English because it _____ useful.    A. is, is          B. is, are            C. are, is          D. are, are 答案：C如下图所示质量为m的物体，用水平细绳AB拉住，静止在倾角为θ的固定斜面上，求物体对斜面压力的大小．