You are presented with the quiz "What does an animal like a mollusk lack that many other animals have?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "mollusks are invertebrates such as the common snail" and "invertebrates are animals who lack a backbone or spinal column". So, what's the best answer to the question?
Available choices:
1). sensory neurons
2). Energy.
3). Bodily water
4). kinetic energy
5). alveoli
6). the skin
7). an organism's body
8). spinal column
8).