Rosemary is studying whether bird-watchers become better at recognizing birds after having studied birdsongs. She tests 5 bird-watchers on their ability to recognize 10 different birds, then has them study birdsongs, and then tests the same 5 bird-watchers on 10 new birds. What is the dependent variable? Group of answer choices Type of birdsong Level of birdsong study Number of correctly identified birdsongs Age of the birdwatcher