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 $17, 17, 20, 20, 23,23,$ and so on.
Every third number follows a second pattern, in which $3$ is subtracted from each number to arrive at the next: $34, 31, 28$
$\text{First Series: $17+3=20$,$20+3=23$}$
$\text{Second series: $34-3=31$,$31-3=28$}$
$\text{Option D}$