Select the most appropriate option to fill in the blank.

The Allies ______ the war in 1945.

won

The most appropriate option to fill in the blank is won.

The sentence is about the Allies winning the war in 1945. The word "won" is the past tense of the verb "win", which means to achieve victory in a contest or competition. It is the most appropriate word to use in this context because it describes how the Allies achieved victory in the war.

The other options are not as appropriate.

• Were winning is the past progressive tense of the verb "win", which means to be in the process of winning a contest or competition. This is not the most appropriate option because the Allies were no longer in the process of winning the war in 1945, they had already won.
• Have won is the present perfect tense of the verb "win", which means to have achieved victory in a contest or competition at some point in the past. This is not the most appropriate option because the Allies won the war in 1945, which is not in the past tense.
• Win is the infinitive form of the verb "win", which means to achieve victory in a contest or competition. This is not the most appropriate option because it does not indicate that the Allies actually won the war.