Which Object from the First or Second Stage Reports Whether

Which object from the first or second stage reports whether an instrument is relevant?

A) Check if the residuals from the first stage regression are uncorrelated with the instrumental variable.
B) Check if the residuals from the second stage regression are uncorrelated with the instrumental variable.
C) Check if the coefficient on the instrumental variable in the first stage is statistically distinct from zero.
D) Check if the coefficient on the instrumental variable in the second stage is statistically distinct from zero.