To express 671,000,000 in scientific notation, you need to move the decimal point so that there's only one non-zero digit to the left of the decimal.
671,000,000 can be rewritten as 6.71 when you move the decimal point to the left 8 places (since there are 8 digits to the right of the first digit).
Thus, 671,000,000 in scientific notation is:
6.71 × 10^8
So the correct answer is:
6.71 × 10^8