若圆锥的轴截图为等边三角形,则称此圆锥为正圆锥,则正圆锥的侧面展开图的圆心角是()
A:90°
B:120°
C:150°
D:180°
In those days, books were produced____ ____.
—— _______city is the capital of China?——Beijing is .