He was late ____ the bad weather.
我看见一只飞蛾不停地不断地扇动翅膀。
如图,在平面直角坐标系xOy中,△ABC顶点的横、纵坐标都是整数.若将△ABC以某点为旋转中心,顺时针旋转90°得到△DEF,则旋转中心的坐标是( )
I don't think it is _____ useless competition, because it has offered us ____valuable experience for the next competition.