The father warned his son that he should be beware of him.

The correct answer is C. The father warned his son, “Be careful about him.”

The other options are incorrect because they do not convey the same meaning as the original sentence. Option A is too direct and does not express the father’s concern for his son’s safety. Option B is too informal and does not sound like something a father would say to his son. Option D is too general and does not specifically warn the son about the man.

The father’s warning is important because it shows that he cares about his son’s safety and wants him to be careful around the man. The son should heed his father’s warning and be careful about the man.