颈椎痛引起头痛怎么办:But we often say hello to a classmate in an informal way .怎么翻译？

But we often say hello to a classmate in an informal way .怎么翻译？ What is that we never borrow but often return? What is that we never borrow but often reture? What is that we never borrow but often return?? what is that we never borrow but often return（归还）? What is that we never borrow but often give back?的答案 What is it that we never borrow but often return?(谜语) we often ( ) there. sing-,we,dance,often,and(.) 脑筋急转弯：.What falls often but never gts hurt?