The correct answer is C. treated lightly.
To make light of something means to treat it as unimportant or not serious. In this case, the man is treating his father’s advice as unimportant and not worth considering.
The other options are incorrect because they do not accurately describe the man’s actions. Option A, followed readily, means to do something quickly and without hesitation. Option B, disregarded, means to ignore or pay no attention to something. Option D, rejected, means to refuse to accept something.
In this case, the man is not following his father’s advice readily, he is not ignoring it, and he is not refusing to accept it. He is simply treating it as unimportant.