Explanation:

- "The murder ______ of Agatha Christie have made her the best-selling novelist in the world."

- Option 1: Mystery

- "Mystery" is singular. It doesn't match with the plural verb "have made."

- Option 2: Mysteries

- Correct Answer: "Mysteries" is plural and matches with the plural verb "have made." It makes sense contextually.

- Option 3: Puzzled

- "Puzzled" is an adjective or past tense of a verb, and doesn't fit grammatically in the sentence.

- Option 4: Poems

- "Poems" doesn't contextually fit since Agatha Christie is known for mystery novels.

- Option 5: Plotted

- "Plotted" is a verb in past tense, inappropriate for the blank in the sentence structure.