Which is the best way to combine sentences two and three

Let me break it down for you, starting with:

A. That was when I realized my decision was final; but there was no turning back. Now, at first glance, this seems like a pretty good answer, right? Wrong, you don't need that "but" there, doesn't it seem a bit out of place? Now, I'm not saying this isn't something you can do, but it's not the best answer choice.

B. That was when I realized my decision was final; however, there was no turning back. "However" is a word that you usually don't see people use a lot.  Now, to me, as someone who likes lengthy writing, I would choose this answer choice, but since it asks for the best answer choice, this one isn't the correct one.

C. That was when I realized my decision was final; also there was no turning back. Anyone with a brain can tell that this is obviously a wrong answer; you wouldn't just say, "Also, there was no turning back." in the middle of a sentence, it doesn't fit there.

D. That was when I realized my decision was final, and there was no turning back. Read this aloud, you can tell that it sounds and slides off the tongue nicer than the other three sentences.

D is the correct answer.

answer: i would say he was very determined and persistent in overcoming obstacles.

explanation:   "the magician of menlo park" as he was called, liked to tell an incident that happened when he was 8 years old and came back home crying after attending school for three months because his teacher called him "sterile and unproductive". from nowadays perspective, we can say that thomas alva edison was one of the most persistent and determined man that has ever existed. when edison was 14, he contracted scarlet fever. the effect of the fever, as well as a blow to the head by an angry train conductor, caused edison to become completely deaf in his left ear, and 80-percent deaf in the other. so as you can see he had to struggle to not so many minor issues but he always succeeded.

is this the question?