By next year, they _____ their new house.
Explanation
By next year, they will have built their new house.اگلے سال تک ، وہ اپنا نیا مکان تعمیر کرلیں گے۔"By next year" indicates a future perfect tense structure."Will have built" correctly expresses an action that will be completed before a specific time in the future.