"What did you do the day before yesterday?"
Hmm. I left out the か and it still marked my answer correct. Is the 何 sufficient to denote a question here?
Duo seems to be giving primarily past tense example sentences that use particles and present/future tense examples that don't use particles--is this a rule or is either structure acceptable regardless of tense?
So I put in the wrong answer, but it said the correct answer would be "おとといは何をしたの？" Is this actually correct? I thought you needed "か" for questions? How does "の" work here? の isn't even something you can select from the word list so I'm pretty skeptical.
Duo's answer is interesting here. Its given you the answer in casual Japanese, incorrectly.
The (no) particle is used as a question marker in casual form speech, you cant really mix the two forms together until you are creating very long and complicated sentences with multiple verbs.
Where duo is wrong here is the conjugation of "masu" form in casual speech. Usually if you were speaking politely (masu form) you would take "to do (su ru)" and change it to (shi) then add (masu). And yes, (ka) is the question marker in polite form Japanese.
So "Will you do it?" would be "(shi masu ka)"
However in casual form Japanese, you keep it as (su ru) and don't add (masu.)
Adding (ta) simply makes it past tense and then adding (no) makes it a question in casual speech.
So it would be "Did you do it?" or "(suru ta no?)" or in this questions case:
"What did you do the day before yesterday?" would be "(ototoi wa nani wo suru ta no?)"
The plain form of する is した、never するた. So in the example above it should be 一昨日は何をしたの？
It's not as simple as just adding た to the dictionary form of a verb, it has to be conjugated. Check out this website for more info on the plain form in past tense: https://www.learn-japanese-adventure.com/japanese-past-tense.html
Afaik yes, as the question, 何,is the direct object. Please educate me if I'm mistaken!