Four curves A, B, C and D are drawn in the given figure for a given amount of gas. The curves which represent adiabatic and isothermal changes are : 

A and B, respectively

As we know that slopes of isothermal and adiabatic curves are always negative ad slope of adiabatic curve is always greater than that of isothermal curve, in the give graph curve A and curve B represent adiabatic and isothermal changes, respectively.