A prime number is defined as the natural number which is only divisible by 1 and itself.
It cannot have any other factors than 1 and itself.
Consider that according t the divisibility rule of 3, the numbers 63 and 72 both yield a sum of digits as 9 which is divisible by 3, so the numbers 63 and 72 will be divisible by 3. Since there exists a factor other than 1 and the number itself, 63 and 72 cannot be prime numbers.
The number 95 contains 5 at its unit place, so the number will be divisible by 5. This is concluded on the basis of divisibility rule of 5. Since there exists a factor other than 1 and the number itself, 95 cannot be prime number.
The last remaining number 73 has no other factors than 1 and 73, so it can be referred as a prime number.
Therefore, option A is the correct choice.