A couple of weeks ago a student and I were talking about systems of public education.  I asked, "What do you think about the quality of public schools in your city?"  The student responded, "It depends of the situation."  Can you find the problem in this sentence?

I addressed this topic in a video with PDF notes on my blog: http://goo.gl/PejU0v

Is the explanation clear?  Do you have any questions?  I am happy to help. :)