Problem:OPTIONS:
- PDAs
- small
- alveoli
- animals
- nerve
- eardrum
- ovaries
- organ

You are presented with the quiz "What tissue do neurons make up?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "cells are organized into tissues, and tissues form organs" and "neurons are the cells of nerve tissue". So, what's the best answer to the question?
****
A: nerve

Problem:OPTIONS:
- an object
- gravity
- density
- bullfrogs
- Energy.
- blastoids
- melting
- volume

You are presented with the quiz "What does not change mass?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "phase changes do not change mass" and "melting is a phase change". So, what's the best answer to the question?
****
A: melting

Problem:OPTIONS:
- virus
- sweating
- bacteria
- sensory neurons
- Exfoliation
- layers of fat
- trees
- Memory cells

You are presented with the quiz "What helps keep people from getting sick?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "active immunity results when an immune response to a pathogen produces memory cells" and "people with weaker immune systems are more likely to get sick from contaminated foods". So, what's the best answer to the question?
****
A: Memory cells

Problem:OPTIONS:
- fur seals
- viruses
- animals
- jellyfish
- bacteria
- ducks
- mammals
- phytoplankton

You are presented with the quiz "What have a nervous system?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "most invertebrates have a nervous system" and "jellyfish and insects are invertebrates". So, what's the best answer to the question?
****
A:
jellyfish