题目

— Do you know ______?— Not sure, but it was on July 13 last year. A . when we started summer vacation B . when we will start summer vacation C . when will we start summer vacation D . when did we start summer vacation 答案：B手电筒、太阳光射出来的光线可以近似地看做（　　）A．直线B．射线C．线段