Which of the following is a composite number?

A composite number is defined as a positive integer that has at least one positive divisor other than one and itself. This means that a composite number can be divided evenly by at least one additional number besides 1 and itself.

In this case, 15 is indeed a composite number because it has divisors other than 1 and 15; specifically, it can be divided evenly by 3 and 5 (15 = 3 x 5). Therefore, it meets the criteria of having multiple divisors.

In contrast, the other numbers mentioned (7, 13, and 19) are all prime numbers, which are defined as numbers greater than 1 that have no divisors other than 1 and themselves. Each of these numbers has exactly two distinct positive divisors. Hence, they cannot be classified as composite.