They have an air of freedom, and they have not a dreary commitment to mean ambitions or love of comfort.（新概念四Lesson5）请问老师，这里不用don't have而是用not a，是not a=no吗，然后后面的or表示否定成分的并列？
...re taught as soon as your Children can understand what you're saying．When your children do something right，let them know．When your children do something wrong，tell them how they should do it and why．Here are some basic manners for children：1．Wait for their turn and don't interr...
...of mass loss. 请问，老师这里用blowing 不用blew 是因为blow的这个用法吗(of air, wind, etc. : to move with speed or force)？，这里的a stream of charged particles和风是同一种“物质”，他们会自发的移动，而不是被吹。off表示离开的意思。