The correct answer is A. quite worthless.
The idiom “not worth his salt” means “not good enough” or “not up to standard.” It is thought to have originated in the Middle Ages, when salt was a valuable commodity. A soldier who was not worth his salt was not worth the cost of the salt that was used to pay him.
In the context of the question, the speaker is saying that if the person fails at this juncture, he will be shown to be worthless. This could mean that he is not good enough at his job, or that he is not a good person.
The other options are incorrect because they do not accurately reflect the meaning of the idiom. Option B, “very proud of himself,” is not a negative statement. Option C, “quite depressed,” is not a statement about someone’s worth. Option D, “very strange,” is not a statement about someone’s worth.