In a language with indefinite and definite articles, have an article that is historically related to the interrogative pronoun/determiner 'what'. Unlike 'what', however, it signifies that a definite noun is the topic of a yes/no-question. In the pseudo-English used to illustrate this, I'll form it analogously to a/an: wha, whan.
you saw wha car?
have you heard whan opera?
the emissary gave wha gift to the king?
the emissary gave a gift to wha king?
wha emissary gave a gift to the king?
A cool thing about this is that definiteness is neutralized in polar questions. Also, other determiners might be forced to behave in quirky ways of the syntax of determiners is anything like that of English:
* you saw wha my car
you saw wha car of mine
(or quirks analogous to that).