The correct answer would be that all of the elements mentioned were part of St. Thomas Aquinas philosophical system. He considered himself an Aristotelian (followed Aristotle's teachings which in modern day are considered the development of Plato's teachings), an Empericist (it is the theory that all knowledge comes from sensory experiences) and a Neoplatonist ( believes mind over matter and that reality is subjective; depends on the highest principle). And since he was before anything a Christian theologian, then all the elements are part of his system.
The second sentence shouldn't start with Since because Since is a word to combine sentences like because combines sentences. They are conjunctions I believe.
