Respuesta :
d. all of the above is your answer.
All of these can indicate that the writer is going to give a cause or reason for the cause to be true.
Finally & Since generally is used to give the reason for the cause, while However is used to counter rebuttals (in most cases).
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I would say "since". You labeled it "c" but you might've meant "b". I'm saying "since" because if you use it in a sentence, the other transitional words can be used in other ways. "However" doesn't indicate a cause or reason but an alternative, and "finally" can be used in many ways, such as a list format.