According to what I know, B is the correct answer.
Answer:
I don't care. Because, if we feel sad, it will be our weakness, our sadness is their strength. I will keep quiet and this will a revenge for them.
Explanation:
The answer to this would be B, because it cannot be used as a sentence by itself. The other three can be used as a sentence without needing another fragment of the sentence. Another example of answer B is that it is a dependent clause, and the other three are independent clauses.
So B is your answer.