What expression is not equivalent to 1/343

A7-1 x 7-2

B.77 x 7-10

C7-2 x 7-5
D7-5 x 72

(All expressions have an Integer either negative or positive u just can't type it correctly here and B and D or not 77 or 72 it's 7 and positive 7 and D is 7 positive 2

Verified Answer :

1 / 343
This is just equal to 
1 / 7^3 = 7^-3

A. 7^-1 7^-2 = 7^(-1 + -2) = 7^-3
B. 7^7
7^-10 = 7^( 7+ -10) = 7^-3
C. 7^-2 7^-5 = 7^(-2 + -5) = 7^-7
D. 7^-5
7^2 = 7^(-5 + 2) = 7^-3

So the correct answer is letter C. 7^-2 * 7^-5