—Where's your brother? I haven't seen him for several days.
—He Tibet for holiday.
A:have been to
B:has gone to
C:went to
如图,抛物线y=﹣x2﹣2x+3与x轴交于A、B两点,与y轴交于点C.
书放在水平桌面上,桌面受到弹力的作用,产生这个弹力的直接原因是()