While deciding where to hunt for specimens, what's the first thing scientists have to consider? Please answerr

for the points

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.

oxygen = 21% of the atmosphere

nitrogen = 78%

carbon dioxide = 0.1%

argon =0.934%

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.