小明在做“探究凸透镜成像规律”的实验时,凸透镜的位置固定不动,实验操作规范.在图示位置时,烛焰恰好在光屏上成清晰的像.
—Did you get up late this morning?
—Yes, so after______quick breakfast, I had to run to office
It was the second time that we ________ in holding such important parties.
一个周角可以分成____ 直角。