Answer:
B.
Step-by-step explanation:
"Things change because they are not complete; but their reality can only be explained as part of something that is complete. It is God."
Rememeber that Aquinas (as most of medieval philosophers) was influenced by Greek philosophers, especially Plato and Aristotle. To better understand why this quote better epxlain Aquina point of view we must remember the Aristotelian natural theology in which Aristotle expose his point of view about God as "the unmoved mover".
The "unmoved mover" concept is very interesting because in it God is not only the creator of all (as we commonly know from the bible), but it is also part of it all:
All that exist´s is created from God; but since all is created from him, everything that exist´s is a part of him, and the whole universe is no other thing than him, fragmented throughout the universe.