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Adrian, Ethel, Glenn, and Joan are each writing compositions in the key of C major. Which composer is using the MOST common chord progression?

1. Adrian is using the I-ii-V progression.

2. Ethel is using the I-ii-iii progression.

3. Glenn is using the IV-V-I progression.

4. Joan is using the vi-IV-V progression.

Glenn is using the most common chord progression in the key of C major, which is the IV-V-I progression.