During a Job Interview, Dario Was Unable to Answer the Interviewer's

During a job interview, Dario was unable to answer the interviewer's final question because it was slightly technical and he did not know the answer. He is worried that this one answer may cost him the job even though the rest of the interview went well. To possibly salvage his situation, Dario should

A) trust that the rest of the interview has gone well and leave the interview as it is.
B) be honest and tell the interviewer that he has let himself down.
C) ask the interviewer if he could answer the question again.
D) restate a positive point that he would like the interviewer to know.
E) apologize to the interviewer before he leaves the interview.