Answer:
D.
Step-by-step explanation:
we see a1 = 6.
that is the starting value. everything else then (to generate the new sequence elements) is added to this.
so, B and C are out.
and clearly, for every new sequence element we add -3. and we do this for every sequence element except for a1. so we add -3 (n-1) times.
therefore, only D is correct.
