Your project concerns writing a new software app to track physical activity such as running, biking, and walking, including time spent on the activity, heart rate, and speeds. You've performed some preliminary testing and discovered some changes need to be made to the code. Once the changes are made, you'll test again to ensure the app is working as expected, starting with logging in, tracking each activity, and measuring each criterion for accuracy. What type of testing does this question describe?

A. Regression B. End‐to‐end C. Unit D. User acceptance