Standard English in a lot of the translations in this course, have been, word for word and frankly some of the translations would never be spoken by a native English person. So to "complain" about "to" and omitting the "to" in this translation makes me smile. The "Can you show me the horse is correct", but OH BOY, some of the other translations into English in the course could do with some revision!
Having Swedish as my native language, montri is a half-way "false friend":
English to mount (that thing you're supposed to do with most of the things bought at IKEA)
[this is the false friend]
Esperanto montroŝranko, aŭ vitrino
English display case
[this is the one I should remember]
... sooo ...
"Can you mount (as in: put it together, build) this horse for me?"
"Al" is necessary here to show the indirect object; to show to whom the horse is being shown.
The horse is the direct object here as it is the thing being shown and therefore takes the -n. "Mi" is the indirect object and so is preceded by "al" here.
Words never take the accusative after prepositions unless they are showing direction. However words never take the accusative after "al" as it already shows direction.
See here for more info on -n.
Just found this out watching Alex Miller on YouTube that you can't say ĉu vi povas montri min la ĉevalon because with indirect objects you have to say it this way ĉu vi povas montri al mi la ĉevalon ? I have a question if you say it this way ĉu vi povas montri ĉevalon al mi does that have the same meaning ?