Figure shows the variations of the internal energy `U` With density `rho` one mole an ideal monatomic gas for thermodynamic cycle `ABCA` . Here process `AB` is a part of rectangular hyperbola,-
A. process `AB` is isothermal & net work in cycle is done by gas.
B. process `AB` is isobaric & net work in cycle is done by gas.
C. process `AB` is isobaric & net work in cycle is done on the gas.
D. process `AB` is adiabatic & net work in cycle is done by gas.