The correct answer is D. unassuming.
Diffident means lacking confidence or assurance. Someone who is diffident may be hesitant to speak up or take risks. They may also be reluctant to draw attention to themselves.
In the context of the question, the man is described as adopting a diffident stand when it comes to his son’s career. This suggests that the man is not confident in his son’s abilities or potential. He may also be worried about his son’s future and what it holds.
The other options are not as accurate descriptions of the man’s attitude. A confident person is sure of themselves and their abilities. A bold person is daring and courageous. A forward person is assertive and outgoing. An unassuming person is modest and humble.
In conclusion, the correct answer is D. unassuming.