700.000 = 7 . 10 . 10 . 10 . 10 . 10
We know that equal bases sum the exponents, so,
7 . 10^(1 + 1 + 1 + 1 + 1)
7 . 10^5 = 700.000
But we can also say:
(7 . 10) . 10^4
or
(70 . 10) . 10³
or
(700 . 10) . 10²
or
(7000 . 10) . 10
As we can see, the alternative C shows (7 . 10) . 10^4 which can be a correct ans, so, alternative C.