Select the correct statements about factors affecting ionisation enthalpy.

1. AAt the same nuclear charge, more inner-shell shielding lowers the ionisation enthalpy
2. BAt constant shielding, a larger effective nuclear charge raises the ionisation enthalpy
3. C$\mathrm{Zn}$ (906) has a lower first ionisation enthalpy than $\mathrm{Cu}$ ($745\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$)
4. D$\mathrm{Tl}$ (589) has a higher first ionisation enthalpy than $\mathrm{In}$ ($558\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$) because of poor shielding by inner $4f$ and $5d$ electrons