The four sentences (labelled 1, 2, 3, and 4) given below, when properly sequenced, would yield a coherent paragraph. Decide on the proper sequencing of the order of the sentences and key in the sequence of the four numbers as your answer.

1.As books age, the cellulose and lignin in the paper begin to break down, releasing a mix of volatile organic compounds into the air.

2.Old books carry a scent that many people instantly recognize—and even love.

3.These compounds are benzaldehyde, which gives off an almond-like scent, vanillin, which smells like vanilla, ethyl hexanol (floral scent), toluene (sweet), and furfural (which has a slightly bready scent).

4.This familiar aroma isn't just dust or mildew; it's actually a result of slow chemical changes happening inside the paper and ink.

The correct answer is 2413.

To determine the correct sequence of the sentences, we need to analyze the logical flow and the connecting links between them to form a coherent paragraph.

Step 1: Identify the opening sentence.
Sentence 2 acts as the perfect introductory statement. It introduces the main subject of the paragraph: the distinct scent of old books that many people recognize and enjoy. It stands independently and sets the context for the rest of the text.

Step 2: Find the sentence that elaborates on the introduction.
Sentence 4 logically follows sentence 2. It uses the phrase "This familiar aroma," which directly refers back to the "scent" mentioned in sentence 2. It clarifies that this smell is not simply from dust or mildew, but rather the result of chemical changes within the book.

Step 3: Detail the chemical changes.
Sentence 1 expands on the "chemical changes" introduced in sentence 4. It explains the specific process involved: as books age, cellulose and lignin break down, releasing "a mix of volatile organic compounds."

Step 4: Conclude with specific examples.
Sentence 3 seamlessly follows sentence 1. It begins with "These compounds," which serves as a direct link back to the "volatile organic compounds" mentioned at the end of sentence 1. It lists specific examples of these compounds, such as benzaldehyde and vanillin, and describes their individual scents, bringing the paragraph to a natural and detailed conclusion.

Following this logical progression, the coherent paragraph is formed by the sequence 2, 4, 1, and 3.