"Any milk or sugar" should be accepted. It pertains to the same partitive notion as "some milk or sugar" the solution shows.
Why again is it 'tai' here instead of 'vai'?
'tai' is when the answer could be either/or, you could have milk, or sugar, or milk and sugar.
'vai' is when it is one or the other, eg hot or cold.
Thank you very much!
"would you milk or sugar?" should also be accepted
"Would you like milk or sugar," that is! But yes, I agree, it should be accepted
'some' feels less normal than 'any' here. Although 'do you want some milk' works ok, when 'or sugar' is added, it makes it a bit odd.
Is "tai" used only for interrogative sentences and "vai" for the others?
I thought the partitive covered the concept of "some." But perhaps because milk and sugar are uncountable, "some milk and sugar" was marked wrong.