There are 15 rows of seats in an auditorium. The first row has 20 seats, and each of the other rows has 5 more seats than the row immediately in front of it. Which of the following is formed by the list of the number of seats in each row?

Each row has 5 more seats than the row before it, so the number of seats increases by a constant difference of 5. A sequence with a constant difference is arithmetic; for example, the first few rows have 20, 25, and 30 seats. Therefore, the list forms an arithmetic sequence.

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