题目

The online game platform is crowded with teenagers, few of _______ enthusiastic about study. A . whom B . that C . who D . them 答案：D 已知命题：“若k1a＋k2b＝0则k1＝k2＝0”是真命题，则下面对a，b的判断正确的是 [　　] A．a与b一定共线 B．a与b一定不共线 C．a与b一定垂直 D．a与b中至少有一个为0