In which interaction is the host harmed? commensalism competition mutualism parasitism

It is 100% Parasitism.

Parasitism is a relationship between two organisms were one organism, or the parasite feeds at the cost of the other organism or host. Ticks and dogs, these are two things a pet owner dreds to see. The tick is considered the parasite because it can get on to a dog and carries diseases with it. One disease is called the Rocky Mountain spotted fever, this can be harmful to the dog and can have it become very ill.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.

the correct answer is b