13 29 15 26 17 23 19

• A. 22 20
• B. 20 17
• C. 20 21
• D. 21 23
• E. 25 27

Answer: (C)

Here, there are two alternating patterns, with every other number following a different pattern. The first pattern begins with 13 and adds 2 to each number to arrive at the next; the alternating pattern begins with 29 and subtracts 3 each time.