Answer:
D
Step-by-step explanation:
Because in D, there no x-value that are repeating in the list.
For example A, the value 8 and -8 are being repeated twice, which makes this relation not a fuction.
On the 4th stage, 81 friends will be called to be told of the news
To reduce the radical, you have to factorize 108.
108 is a multiple of 3, so to factorize it, you can divide it by 3

You can rewrite the square root as:
![\sqrt[]{3\cdot36}=\sqrt[]{3}\cdot\sqrt[]{36}](https://tex.z-dn.net/?f=%5Csqrt%5B%5D%7B3%5Ccdot36%7D%3D%5Csqrt%5B%5D%7B3%7D%5Ccdot%5Csqrt%5B%5D%7B36%7D)
The square root of 36 is equal to 6 so you can write the expression as: