A 35 year old man with opioid use disorder is being treated with 16mg of buprenorphine daily. He is abstinent from opioids, which has been confirmed by negative urine toxicology results, however his urines are intermittently positive for benzodiazepines and he notes drinking alcohol two days per week. Further history, corroborated by his wife, indicates that he drinks 2-4 beers, 2-3 days a week and feels intoxicated. He says he wants to stop drinking altogether and has tried, however hasn't been able to quit, as he experiences cravings after a day or two. The drinking worries his wife, but otherwise his marriage, work and their social activities have not been affected by it. He's had no health problems associated with drinking and no history of tolerance or alcohol withdrawal when he does not drink for a few days. What is the most appropriate DSM-5 diagnosis?

A. Substance-induced anxiety disorder.

B. Unspecified anxiety disorder.

C. Benzodiazepine use disorder, mild.

D. Benzodiazepine use disorder, moderate.

E. Benzodiazepine use disorder, severe.