We didn’t use to swim in that river.
Did we(you) use to swim in that river? Yes,we did.
She didn’t use to send parcels from Moscow.
Did she use to send parcels from Moscow? Yes.she did.
Mary didn’t use to live in China but now she lives in Russia.
Did Mary use to live in China? Yes.she did.
Those boys didn’t use to be enemies.
Did those boys use to be enemies? Yes,they did.
I didn’t use to read in the evenings.
Did you use to read in the evenings? Yes,I did.