"Do you like tennis or soccer?"
Translation:¿A ti te gusta el tenis o el fútbol?
¿Te gusta el tenis o el fútbol? = Do you like tennis or soccer?
"A-phrases” are used to clarify or emphasize object pronouns.
Since the indirect object pronoun te is as clear as can be, Duo's "a-phrase" must be there to emphasize the te. Nothing in the context asks for emphasis, so the sentence should be accepted as correct without the "a-phrase."
Adding the "a-phrase" here doesn't change the translation, unless you want to show the emphasis in your English translation with italics, underlining, etc.: "Do you like tennis or soccer?"
"A-phrases" are very important when they add information (clarify) the object pronoun:
Le gusta el tenis. He/She/You (formal) like(s) tennis.
A él le gusta el tenis. He likes tennis.
A ella le gusta el tenis. She likes tennis.
A usted le gusta el tenis. You like tennis.
When I see or hear a ti, I think, "And how about you? Do you like tennis or soccer (like I do?)" It often suggests the questioner is looking for agreement or comradery.
my response was "te gusta tenis o futbol?" and i got it wrong because I needed el before tenis. However, correct response did not put el before futbol. Why not both?
I put el before both as illogical otherwise. Not only accepted, it is given as the correct answer now. Must have been an error. The articles are def required I think because we mean tennis or football in general and they are actually the subjects of this, to English ears, back-to-front sentence.
I am agree with Bruno and you. I am from a latin American country. And if you want you can say "tenis y fútbol" or "el tenis y el fútbol".
I agree with Marcy Brown. Only reason for "a ti" is if the object is to use as many of the mult choice words as possible that they give you in the sentence. Unnecessary here.
'There seems to be another good reason: the computer thinks it's wrong if you don't !