Answer:
C) cannot be simplified
Explanation
We want to simplify the radicals:
![\sqrt[3]{7} - \sqrt[4]{7}](https://img.qammunity.org/2021/formulas/mathematics/middle-school/f5t3l4r6gqhcrgrd4rnq8lln2np7hqc1sm.png)
We can rewrite this as exponents:

Since the base are the same but are subtracting, we do not have any rule of indices for subtracting unlike indices .
Therefore the expression cannot be simplified further.