The correct answer is C) rounded. Excessive pressure on the ends of a file will cause the work surface to become rounded. This is because the file teeth will wear down and become less sharp, creating a rounded profile on the file's working surface. This can negatively impact the file's ability to efficiently remove material from the workpiece. The other options are incorrect because: A) smooth is the opposite of what happens, B) rough is not the primary effect, and D) tapered is not an accurate description of the file's deformation under heavy pressure.