Which of the following is the negation of statement “a*b = b*a for every real number a and b”?

• A. a*b ≠ b*a for every real number a and b
• B. a*b = b*a for every real number a or b
• C. There exists real number a and b for which a*b ≠ b*a
• D. There exists real number a and b for which a*b = b*a