The heart along with the rest of the circulatory system could be compared to
a major transportation system in a city
a chemical manufacturing plant
the police department in a city
a recycling plant

the correct answer is:

a population changes in response to a change in the environment.

bacteria could be both, harmful and to us. harmful bacteria could make us sick and probably even by getting the chances of getting a disease, but good bacteria fight it off with your immune system. there is always bacteria everywhere we go. we need to make sure to wash our hands after using the restroom, before eating, after eating, after petting an animal too. so you see, bacteria is everywhere and is harmful or . i hope this . : ) : ) : )