Which of the following is a characteristic of a proper fraction?

A proper fraction is defined as a fraction where the numerator (the top number) is less than the denominator (the bottom number). This characteristic means that a proper fraction can take on values that are greater than zero but less than one. For example, in the fraction 3/5, the numerator 3 is less than the denominator 5, making it a proper fraction that clearly lies between 0 and 1.

The other options do not accurately reflect the nature of proper fractions. A proper fraction cannot be equivalent to a whole number, as that would require the numerator to be equal to the denominator or greater, which conflicts with the definition of a proper fraction. While a proper fraction is composed of integers in its numerator and denominator, the statement that it is "only composed of integers" doesn't specifically define a proper fraction but rather describes the types of numbers that are involved in fractions generally. Additionally, a proper fraction does not contain a whole number component; it consists of just a fraction itself without any integer part. Thus, the defining characteristic of being greater than zero but less than one is what makes option A correct.