It's just the formal you. It doesn't differentiate between singular and plural.
du (accusative: dich; dative: dir) = you (informal, addressing one person)
ihr (accusative: euch; dative: euch) = you (informal, addressing more than one person)
Sie (accusative: Sie; dative: Ihnen) = you (formal, addressing one or more people)
As a native English speaker, I do not understand why this is not correct English. There is nothing incorrect about using the terms "tour leader" or "trip leader." Using "leader" rather than "guide" suggests that the "Reiseführer" is a person with some authority over those being led, perhaps a teacher or boss, and is thus consistent with the German "Führer."
(Using "leader" rather than "guide" suggests that the "Reiseführer" is a person with some authority over THOSE being led, perhaps a teacher or a boss).. They translated as "travel guide" = booklet. It seams more apropiate, for a single person, to own a booklet than to own another person especially when that person is supposed to lead her.
okay, there are three choices on the hover: (1) travel guide, (2) guide, and (3) tour guide. I used "guide" and "tour guide" and BOTH were marked wrong in spite of the fact that both are perfectly acceptable in everyday use. In fact, the third alternative sounds clumsy. So what is wrong with tour guide, or guide, anyway? If you sprinkle red herrings to entrap hapless learners, I suggest you check them out in "normal" usage first. 8(