The question 4 includes 3 small questions. Let’s solve it step by step. First of all, question a asks to use the Ratio Test, so thies question must be connected with Ratio Test. Accoding to Ratio Test, we have find the rate of change in the series of sequence. If the rate of change is smaller that 1, definitely the sequence will become smaller and the series will be converges. For solving question b, we can use comparison test, whcih cound be used to distinguish whether the function converges or not by using the result we get from question a.  Compare with question b, the only difference is there is negative possibility in question c, which means the Alternating Series Test can be used in this question.