Which of the following does not have a vaccine available? inflienza mumps measles aids

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.

i might be wrong but i think its a. let me know if i’m right and have a good rest of your day!