They bought a new car last week.
They didn't buy a new car last week.
Did they buy a new car last week?
They bought a new phone one day. (вопрос когда, поэтому добавила one day - однажды, хотя можешь оставить до phone)
They didn't buy a new phone. (здесь подразумевается, что не купили - не купили никогда, поэтому one day и другие обозначения времени не нужны)
When did they buy a new phone?
He was at the zoo last weekend.
He wasn't at the zoo last weekend.
Was he at the zoo last weekend?
Last weekend he was somewhere. (был где-то, опять же, потому что вопрос - где)
Last weekend he wasn't anywhere. (нигде)
Where was he last weekend?
1) Yesterday I went to the cinema and I was very happy.
My mom bought me a new book "Dandelion Wine"
2) I don't have an expensive computer
He wasn't so cheerful last year
3) Did you go to university yesterday?
Did he call you last week?