What is the greatest positive integer x such that 3^x is a factor of 9^9?	Choose the correct choice from the following choices
A) 5	B) 9	C) 10	D) 18	E) 30
What is the greatest positive integer x such that 3^x is a factor of 9^9?   9^9 = (3^2)^9 = 3^18   D. 18
<result>D</result>
What is the greatest positive integer x such that 3^x is a factor of 9^9?