Answer:
Although she was tired, she read until midnight.
Explanation:
The word "although" is a subordinating conjunction that presents a dependent clause. It is used to present a statement that contrasts the main idea of the sentence, introducing the dependent clause to complete the information of the independent clause.
So, the given sentence "_______ she was tired, she read until midnight" presents two contrasting yet connected sentences. While "____ she was tired" presents the contrast in the final clause "she read until midnight", using "although" will complete the whole sentence.
Thus, the final sentence will be "Although she was tired, she read until midnight."
