У Вас ошибка в предложении.
My parents bought their car in Moscow last year.
My parents bought their car in Moscow last year, didn't they?
Did my parents buy their car in Moscow last year?
Who bought their car in Moscow last year?
Did my parents buy their car in Moscow or in Saratov last year?
What did my parents buy in Moscow last year?
When did my parents buy their car in Moscow?
Where did my parents buy their car last year?