按分插秧原理插秧机可分为？
参考答案：
滚动直插式插秧机和往复直插式插秧机。
The teacher asked the students to make their own ______in pairs. They can talk about anything they like. [ ]
A. minds
B. conversations
C. words
D. opinions
特种文献不包括（）。
A.专利
B.标准
C.学位论文
D.期刊
