$nC\Delta T = \Delta Q \rightarrow C = \large\frac{\Delta Q}{n \Delta T}$

For an adiabatic process, $\Delta Q =0$, so heat capacity has to be zero.

For an isothermal process, $\Delta T = 0$, so heat capacity is infinite as no finite heat capacity will result in heat change, and also it depends on the nature of the gas and process.

Therefore, (D) is the appropriate answer.