To replace the italicized phrase and make the given sentence grammatically correct, let's analyze the options:
Upon evaluation, Option B: "speak for itself" is the most fitting option to replace the italicized phrase in the sentence. Therefore, the correct sentence should read:
I don't think you need to explain the situation, your conduct speak for itself.
In conclusion, the correct idiomatic expression "speak for itself" is used to imply that the situation or conduct is self-explanatory and does not need further clarification.