Necessary to explain research findings. a. variables b. research models c. theories d. symbols

C. Theories

Explanation:

Theories basically explain why of research findings. By definition, theories help us understand, explain, and predict the occurrence of a phenomena. In research, theories support research findings by explaining how the variables involved influence each other not merely based on observation during this one experiment. It also helps validate the findings by relating it to theories of previous work.

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answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.