The correct sentence is (A). In this example the author stablishes a good parallel structure when he/she enumerates the items. Commas must not be used in an independent clause; in particular, before a verb (the comma before “were” is not correct as an example B).
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Answer:
Animals are used in scientific research to help us understand our own bodies and how they work. This is necessary to develop new medicines. Animals are also used to safety test potential medicines before they are tested in people and to check the safety of other chemicals.
Explanation:
I'd say the third sentence sounds very supportive, it supports the idea and positivity that service brings.
