Select the most appropriate option to fill in the blank.

I walked out ______ I wanted to breathe some fresh air.

because

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

The word because is used to introduce a reason or explanation for something. In this case, the sentence is saying that I walked out because I wanted to breathe some fresh air. This means that the reason I walked out was because I wanted to breathe some fresh air.

The other options do not make sense in the context of the sentence.

• But is used to introduce a contrast or contradiction. It cannot be used in this sentence because it does not convey the same meaning of "a reason or explanation for something".
• That is used to introduce a statement or clause that provides more information about something. It cannot be used in this sentence because it does not convey the same meaning of "a reason or explanation for something".
• Yet is used to indicate that something has not happened or been done, even though it was expected to happen or be done. It cannot be used in this sentence because it does not convey the same meaning of "a reason or explanation for something".