1.  17 17 34 20 20 31 23

A. 26 23
B. 34 20
C. 23 33
D. 27 28
E. 23 28

Answer: Option E

Explanation:

This is an alternating subtraction series with repetition. There are two different patterns here. In the first, a number repeats itself; then 3 is added to that number to arrive at the next number, which also repeats. This gives the series 17, 17, 20, 20, 23, and so on. Every third number follows a second pattern, in which 3 is subtracted from each number to arrive at the next: 34, 31, 28.