A:当时社会的焦点问题是奴隶制的存废
B:美国社会不稳定
C:奴隶制变成美国向往的制度
D:种族问题严重
关于太阳系的叙述,下列说法中正确的是( )
— Lily, look, a crowd of birds are flying to our small yard.
— Just now, I threw some bread in the yard. They have come here for the food.