题目

E Should struggling students be banned from clubs and sports? Getting a bad grade in Rockingham, Vt. could get you kicked off the team! School officials there are considering new guidelines that would prevent students with bad grades from participating in extracurricular activities, such as sports and clubs. The proposal would affect students in eighth grade and below. School board member Mike says the policy would motivate students to work harder in school. He drafted a letter to coaches, parents, and after-school program leaders to encourage them to allow only kids who are meeting certain ac20世纪中叶科学家发明了红光LED和绿光LED，为与这两种LED组合，产生白色LED光源，日本科学家又探寻到一种LED，它是( )A. 紫光LED B. 黄光LEDC. 蓝光LED D. 橙光LED C 【解析】光的三原色是红、绿、蓝，红光LED、绿光LED、蓝光LED组合能产生白色LED光源。故选：C.