To determine the discharge at a section in a stream from its rating curve, the required data are_______________?

To determine the discharge at a section in a stream from its rating curve, the required data are_______________?

1) slope of water surface at the section
2) stage at the section
3) current meter readings at the section
The correct answer is?
A. (1) and (2)
B. (2) and (3)
C. only (2)
D. only (3)