ANS:A - first stage

I think, in classic 3 stage opamp amplifier gain i.e Vout/Vin1-Vin2 equals 1+2R2/R1 (potentiometer). And therefore gain totally depends on r2 which is the feedback resistor for first opamp and the common pot r1.

Whereas it's dependence on pot is non-linear so they modified it by adding an additional opamp to get a linear gain.