题目

如图，为了研究钟表与三角函数的关系，建立如图所示的坐标系，设秒针尖位置.若初始位置为，当秒针从（注此时）正常开始走时，那么点P的纵坐标y与时间t的函数关系为 A．           B． C．           D． 答案：C 时刻，经过的圆弧角度为，则以轴正方向为始边，所在射线为终边，对应的角度为，则对应的角度为，由可知在单位圆上，所以时刻的纵坐标，故选C Last year, five Chinese teachers to a school in the UK to teach the British students in Chinese style for four weeks.A. was sent B. were sent C. have sent D. sent