喷洒在蔬菜上的农药一般很难渗入蔬菜的细胞内,从细胞结构看,其主要原因是( )
A:细胞壁
B:细胞膜
C:细胞质
D:细胞核
—What about _____ English-Chinese dictionary on the bookshelf?—In my opinion, it's _____ useful tool book for my English learning.
—How are you?
—I'm fourteen.