Q: Fact 1: Most invertebrates have a more complex nervous system. Fact 2: Invertebrates are animals without a backbone. Given the two facts above, what have more complex nervous systems?

pick from the following.
[1]. animals without a backbone.
[2]. the wearing away of rock.
[3]. h2o.
[4]. barks and snarls.
[5]. plants.
[6]. density.
[7]. Veins and arteries..
[8]. remains of prehistoric life.
The answer is:
[1].