某同学用显微镜观察洋葱鳞片叶表皮细胞,看到了以下几幅图象,这几幅图出现的先后顺序是( )
A:①→④→②→③
B:④→③→①→②
C:③→④→②→①
D:②→①→③→④
—Has Jack finished painting the picture yet?—I've no idea. But he______ it the whole afternoon.
—I worked as a volunteer in the school library last Friday afternoon.
—Really? Can I go with you next time?