I'm sure the interviewer was looking for the previous answer, but in reality the solution would start with evaluating why the query is not using the index that is apparently best. There will be a reason, the query optimiser is very good these days.
A poorly chosen hint will hurt performance terribly.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability