Let's convert the task into an example, simplifyng which will make us able to get the answer.
So, according to the task: [tex] \sqrt[9]{x} * \sqrt[9]{x} * \sqrt[9]{x} * \sqrt[9]{x}
= \sqrt[1/ 9 ]{x} * \sqrt[1/9]{x} * \sqrt[1/9]{x} * \sqrt[1/9]{x} [/tex]
Now we can simplify: [tex] \sqrt[1/9]{x} + 1/9+1/9+1/9
= x^{4/9} [/tex]
So the answer is C:x to the four ninths power