A:商业区
B:工业区
C:住宅区
D:文教区
如图,抛物线y=ax2+bx﹣3经过点A(2,﹣3),与x轴负半轴交于点B,与y轴交于点C,且OC=3OB.
— Would you like some coffee?— No, thanks. I drink coffee. Coffee is bad for my stomach.
入射光线与镜面的夹角是30°,则入射光线与反射光线的夹角是____ 度,如果入射光线垂直射到镜面上,那么反射角是____ 度.