Consider the series 3 + 5 + 7 + 9 + + 2n + 1. write sk and sk+1 a. sk=k(2k); sk+1=(k+1)(k+2) b. sk=k(k+2); sk+1=(k+1)(k+2) c. sk=k(2k); sk+1=(k+1)(k+3) d. sk=k(k+2); sk+1=(k+1)(k+3)