17.it can be said that vaccines do not actually prevent infection. using information learned in previous activities, explain this statement.

Vaccines don't prevent infection it just helps your body to know how to fight a certain infection if/when it enter the body. A vaccine gives your body a tiny amount of a certain antigen so that the body can find the right way to fight it and keep some memory b cells to fight it if the need should arise. Say a person has been vaccinated against the flu and that strain enters their body, they still have it but there body has already seen it and can fight the infection off (hopefully) before you get sick and notice any symptoms.

i think that d. wind is the answer.   i missed the question when i answered a. currents.

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.