The correct answer is A

Explanation

Choice (A) is correct. If this term were inserted into the sentence, the sentence would read “Ray was an inveterate gambler who had seldom gone a day without indulging in his expensive habit.” The term “inveterate” describes something that is established by a persistent habit. If Ray had “seldom gone a day” without gambling, one could certainly say that gambling was his persistent habit. Therefore, it makes sense to describe Ray as “an inveterate gambler.”