A:Ann always takes a dictionary with her.
B:Ann owns many dictionaries.
C:Ann knows many words.
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从超市买来的新鲜蔬菜用保鲜袋装起来,可以延长储存的时间,其主要原因是( )
设M={x|0≤x≤4},N={y|﹣4≤y≤0},函数f(x)的定义域为M,值域为N,则f(x)的图象可以是( )