Задайте вопросы к предложению : They bought a present for their mums birthday the day before yesterday.
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Did they buy a present for their mum's birthday the day before yesterday?
Did they buy a present for their mum's birthday the day before yesterday or last week?
What did they buy for their mum's birthday the day before yesterday?
When did they buy a present for their mum's birthday?
Why did they buy a present the day before yesterday?
Where did they buy a present for their mum's birthday the day before yesterday?