Answer:
The simplified expression of
is 7² ⇒ C
Step-by-step explanation:
Let us revise some rules of exponent
= 
Let us solve the question
∵ The expression is 
→ By using the first rule above add the exponents of 7
∴
= 
∴
= 
→ By using the second rule above, subtract the exponents of 7
∵
= 
∴
= 7²
∴ The simplified expression of
is 7²