Select the most appropriate option to fill in blank no. 4.
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1, i.e., through.
Filler Concept: We need a preposition showing the means or channel used.
Meaning Explanation: “Through” indicates using agents as a channel to sell books.
Grammar Explanation: It correctly describes selling books via agents.
Correction: and also through agents.
Final Sentence: and also through agents.
Conclusion: The correct answer is “through.”