Alberto is stacking firewood. He puts 20 logs on the bottom row. Then he stacks each row so that there is 1 fewer log than the row below. Which of the following can be used to determine the total number of logs in 10 rows?

The rows contain 20, 19, 18, and so on, decreasing by 1 log each time. Because the number of logs changes by a constant difference, these row counts form an arithmetic sequence, and their total is an arithmetic series. Therefore, the correct choice is an arithmetic series.

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