The bench was so long that all of us were able to sit on it.
The bench was long enough __for__ _all___ __of__ __us___ _to___ __sit__ __on__.
I think that it is important to master a foreign language.
I think __it's__ _important___ _to___ __master__ a foreign language.
Mother didn't do the work for her little son ,but taught him how to do it.
Instead of __doing__ _the___ _work___ for her little son,she taught him how to do it.