题干
281. The shop______ its summer stock to be ready for the new winter goods.
A：sold out
B：sold dow
C：sold off
D：sold short
答案(点此获取答案解析）
A
A：sold out
B：sold dow
C：sold off
D：sold short
棱镜的表面，经过三棱镜的折射后发生色散现象，在光屏的ab间形成一条彩色光带。下面的说法中正确的是
