Answer:
It is the last one yet again!
Step-by-step explanation:
If you notice, the first answer is incorrect because it uses a period but then continues like the sentences are connected with a comma.
The second is the same mistake, since there is a period, the reader would figure the subject they were talking about, in this case, homework, is done being talked about.
The third one is kind of the same mistake, but with more depth. The "I" at the beginning is not capitalized and the period placement makes it so there is no filler word on why you scored well on your test, for example,
"I did my homework, therefore scored well on my test."
The last one is correct, even though the I" is not capitalized, I'm going to assume that was an accidental mistake and that in the original problem, the "I" is capitalized. The last sentence has a filler word, just like the one above was missing, therefore it is the right answer.