Consider the systems, each consisting of m linear equations in n variables.

I. If m < n, then all such systems have a solution
II. If m > n, then none of these systems has a solution
III. If m = n, then there exists a system which has a solution 

Which one of the following is CORRECT?

 A I, II and III are true B Only II and III are true C Only III is true D None of them is true

 Only III is true