Q: Fact 1: Arthropods are the largest phylum of invertebrates. Fact 2: Invertebrates are animals without a backbone. Given the two facts above, what don't arthropods have?

Available choices:
a). an exoskeleton;
b). legs;
c). Bodily water;
d). Damaged hearing;
e). kinetic energy;
f). a backbone;
g). Energy;
h). backs;
The answer is:
f).