If n is a positive integer, the notation n ! (read " n factorial") is used to represent the product of the integers from 1 to n inclusive. For example, 5!=1 \times 2 \times 3 \times 4 \times 5=120. Which of the following is equal to a perfect square?
Answer Choices
A. \frac{(20!)(19!)}{1}
B. \frac{(20!)(19!)}{2}
C. \frac{(20!)(19!)}{3}
D. \frac{(20!)(19!)}{4}
E. \frac{(20!)(19!)}{5}