If I can help_______, I don't like working late into the night.
______the Internet is of great help, I don’t think it’s a good idea to spend too much time on it.
It is difficult for us to learn a lesson in life______we’ve actually had that lesson.
“You can’t have this football back_____you promise not to kick it at my cat again.” the old man said firmly.
environmental damage is done, it takes many years for the ecosystem(生态系统)to recover.
____, he talks a lot about his favorite singers after class.