There are two things that cause ocean water to become denser, and those are b) the salinity of water and low temperatures.
The more salt there is, the denser the water will be - take the lake Dead Sea in Israel, Jordan, and Palestine for example.
And the lower the temperature, again, the denser the water will be - the deeper you go into an ocean, it will be more difficult to move around due to density and other things.
The statement '(a) there are billions of galaxies in a galaxy cluster' accurately describes a relationship between two parts of the universe.
<h3>What is the solar system?</h3>
The solar system can be defined as a group of billions of galaxies that form a cluster due to gravitational forces that maintain all these celestial bodies linked together. This system contain our Sun.
In conclusion, the statement '(a) there are billions of galaxies in a galaxy cluster' accurately describes a relationship between two parts of the universe.
Learn more about galaxy clusters here:
brainly.com/question/955851
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Gel electrophoresis is a technique used to separate DNA fragments according to their size. This is from Khan academy so I believe it is reliable.