The answer is the option C and the option D, which are:
C. Double the number of pages in the book.
D. The age of my friend.
The explanation for this problem is shown below:
By definition, a variable is an unkown quantity. In the Option A the quantity is given: 
seconds in a minute. In the option B you know the quantity too, which is 
years old. But the option C and the option D does not give any quantity, you don't know the number of pages in the book or the age of the friend yet. Therefore, the answer is the options C and D.
<span>
The good answer is 9
(9:9=1 and 27:9=3)</span>
Step-by-step explanation:
if a^2 +b^2 <c^2,
then abc is not a right triangle since for a right triangle a^2+ b^2 = c^2
f ( - 2 ) = 5 × 3^( - 2 )
f ( - 2 ) = 5 × 1/9
f ( - 2 ) = 5/9
