Unfortunately, it is not a natural sentence either way. Perhaps it was written by a French speaker? This is the natural utterance: You can choose either beef or fish.
In conversation, where complete sentences are less common, you would hear this:
Pasenger: What's the entree? Flight Attendant: Either bee
Thank you fro your answer Micawber. The workbook is produced and sold in Japan... I guess they don't have much proof readers because I found at least 4 other mistakes on the same page