Histamines are chemicals released by the body as an allergic response.They help the body by reacting when their are "intruders" so when enters, histamine acts as a messenger and sends out a signal for the body to create a reaction helping to get rid of teh intruder through some type of reaction.
The 10% rule means that when energy is passed in an ecosystem from one trophic level to the next, only 10% of the energy will be passed on.
3 is the correct answer. Let me know if you want me to explain why that is the answer.