  While it has been recently demonstrated that, for quasi-2D electron gas
(Q2DEG) with one filled miniband, the dynamic exchange $f_x$ and Hartree $f_H$
kernels cancel each other in the low-density regime $r_s\rightarrow \infty$ (by
half and completely, for the spin-neutral and fully spin-polarized cases,
respectively), here we analytically show that the same happens at arbitrary
densities at short distances. This motivates us to study the confinement
dependence of the excitations in Q2DEG. Our calculations unambiguously confirm
that, at strong confinements, the time-dependent exact exchange excitation
energies approach the single-particle Kohn-Sham ones for the spin-polarized
case, while the same, but less pronounced, tendency is observed for
spin-neutral Q2DEG.
