呼吸功能异常易引起的错位是（） A.单侧后牙反 B.后牙锁 C.佝偻病 D.下颌后缩

在操作液压支架的过程中，当支架的前柱和后柱单独升降时，应注意什么问题？

Where do I write the address _______ this postcard?[ ]

A. in                    

B. at                

C. on

The Canadian friends from our school have given us a lot of books, few of ________ a bit difficult for us Chinese students.