  Resistively Detected Nuclear Magnetic Resonance (RD-NMR) has been used to
investigate a two-subband electron system in a regime where quantum Hall
pseudo-spin ferromagnetic (QHPF) states are prominently developed. It reveals
that the easy-axis QHPF state around the total filling factor $\nu =4 $ can be
detected by the RD-NMR measurement. Approaching one of the Landau level (LL)
crossing points, the RD-NMR signal strength and the nuclear spin relaxation
rate $1/T_{1}$ enhance significantly, a signature of low energy spin
excitations. However, the RD-NMR signal at another identical LL crossing point
is surprisingly missing which presents a puzzle.
