Which statements correctly describe the Joule-Thomson effect for a real gas?

Throttling through a porous plug is carried out at constant enthalpy (A true). An ideal gas has no intermolecular forces, so its temperature does not change and ${\mu }_{JT}=0$ (B true). ${\mu }_{JT}=(\partial T/\partial P{)}_H$; since pressure falls on expansion, a positive coefficient means $T$ falls (C true). The inversion temperature is $2a/Rb$, not $a/Rb$ (D false).