Abe, Beth, Carl, and Duncan are four siblings, among which Abe and Carl are twins, and Beth and Duncan are also twins. When the present ages of the four siblings are multiplied, the product is 900. If Beth is older than Abe, what is the age of Duncan? Assume the ages of all siblings to be integers.

(1) The difference between Beth’s age and Abe’s age is a prime number.

(2) If Carl had been born four years earlier, the difference between Duncan’s age and Carl’s age would have been a prime number.

Answer: C

Source: e-GMAT