Arnold and Danny are two twin brothers that are celebrating their birthday. The product of their ages today is smaller by 15 from the product of their ages a year from today. What is their age today?	Choose the correct choice:
A) 2 .  B) 4 .  C) 5 .  D) 7 .  E) 9 .

Rationale: "ad = ( a + 1 ) ( d + 1 ) - 15 0 = a + d - 14 a + d = 14 a = d ( as they are twin brothers ) a = d = 7 d is the answer"
Answer: D