题目

He cut the apple ________, and gave the big to his little sister.    A. into half        B. into halves     C. in halves       D. in the half   答案：B如下图所示，某同学在光具座上做凸透镜成像实验时，光屏上恰成一个清晰的像，则可知该凸透镜的焦距f一定在________cm至________cm之间．