A:learn
B:learned
C:to learn
D:learning
_______ the teacher was very busy, _______he still helped me with my English.
与家蚕发育过程相比,蝗虫不具有的发育阶段是( )
提示:联系生活实际,谈谈三者之问的关系,说说你的看法。
把20克盐放入200克水中,盐和盐水的比是( )