So,
The prime numbers from 1 to 50 are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47.
Group A contains 15, which is a composite number (3 * 5).
Group B contains 49, which is a composite number (7 * 7).
Group C contains 9, which is a composite number (3 * 3).
Group D contains no composite numbers. They are all prime.
Group D contains only prime numbers.