If the HCF and LCM of two rational numbers are equal, then the numbers must be:

Given:
The HCF and LCM of two rational numbers are equal.

HCF (Highest Common Factor): The largest number that divides both given numbers.
LCM (Least Common Multiple): The smallest number that is a multiple of both given numbers.

The Highest Common Factor (HCF) and Least Common Multiple (LCM) of two numbers are typically not equal unless both numbers are the same. The only case where the HCF and LCM are equal is when the two numbers are equal to each other. In that case, the HCF and LCM of both numbers are equal to the number itself.
Equal: If two numbers are equal, their HCF and LCM will both be equal to the number itself.
Composite: This term refers to a number having divisors other than 1 and itself, which is irrelevant in this context.
Co-prime: Co-prime numbers have an HCF of 1, which would not make the HCF and LCM equal.
Prime: A prime number's HCF with itself is the number itself, but this condition does not apply to the equality of HCF and LCM of two different numbers.

So, then the numbers must be equal.

Thus, the correct answer is (a).