题目

两种单色光由水中射向空气时发生全反射的临界角分别为θ1、θ2，已知θ1＞θ2。用n1、n2分别表示水对两单色光的折射率，v1、v2分别表示两单色光在水中的传播速度，则( )A. n1<n2，v1<v2B. n1<n2，v1>v2C. n1>n2，v1<v2D. n1>n2，v1>v2 答案：【答案】B【解析】试题根据临界角公式和折射率与光速的关系式分析可知：若θ1＞θ2，则nl＜n2，v1＞v2．故B正确，ACD错误．故选B． Tommy was planning to buy a car the next week, ________ he ________ enough for a used one． [　　] A．by that time; had saved B．by which time; had saved C．by that time; saved D．by which time; has saved