I think getting a C grade at Mathematics GCSE is not too difficult. Everyone is good in one particular subject, and therefore the Government gives you the opportunity to select the subjects that you enjoy the most, or get good grades, for A-levels. If you didn't enjoy mathematics at GCSE, you won't carry on. C grade is provided to students where they are able to solve real-life mathematical questions that may appear in your life. I think it's fair. The higher B/A/A* grades are gained by students that have an interest to the subject.