3. You do not need to prove an item is true (just saying true is enough for full credit), but you must give a counter example in order to demonstrate an item is false if you want full credit. To give a counter example, give values for T1(N), T2(N), and f(N) for which the statement is false. Suppose T1(N) = O(f(N)) and T2(N) = O(f(N). Which of the following are true? a. T1(N) + T2(N) = O(f(N)) b. T1(N) - T2(N) = o(f(N)) c. T1(N) / T2(N) = O(1) d. T1(N) = O(T2(N))