0) Assume that an > 0 for all n E N and an+1 100. Consider the series E(-1)n41 an n=1 k with k-th partial sum Sk = (-1) tian. n=1 Which of the following statements are true? a) The series converges if and only if lim an = 0. n-+ 00 b) If _ (-1)n+lan converges to S, then S12