Final answer:
The sentence 'My mother told us to clean the kitchen, but we forgot' is a compound sentence because it contains two independent clauses joined by the coordinating conjunction 'but'.
Step-by-step explanation:
The sentence in question is 'My mother told us to clean the kitchen, but we forgot.' This is a compound sentence because it contains two independent clauses joined by a coordinating conjunction. An independent clause contains a subject and a verb and can stand alone as a full sentence. In this case, 'My mother told us to clean the kitchen' is one independent clause, and 'we forgot' is the second independent clause. The coordinating conjunction 'but' connects these two clauses.
Thus, the correct classification for the sentence is Option C: Compound; the sentence contains a coordinating conjunction.