Fill in the blank with the most appropriate word.He ________ an aspirin half an hour ago.

Answer: Option C

In the sentence, "He took an aspirin half an hour ago," the past simple tense is used to describe an action that was completed in the past. The correct form for the sentence is "He took an aspirin half an hour ago."

The other options are not suitable because they do not use the correct verb form or tense:

Option A: takes
This option uses the present simple tense, which is not appropriate for describing a past action that was completed.

Option B: is taking
This option uses the present continuous tense, which is not suitable for describing a specific action that occurred in the past.

Option D: taken
This option uses the past participle form of the verb "take," which is not appropriate for the context of the sentence.

Therefore, the correct answer is Option C: took.