  In previous papers we proposed a model that high-frequency quasi-periodic
oscillations (QPOs) observed in black-hole and neutron-star X-ray binaries are
disk oscillations (inertial-acoustic and/or g-mode oscillations) resonantly
excited on warped disks. In this paper we examine whether time variations of
the QPOs and their frequency correlations observed in neutron-star X-ray
binaries can be accounted for by this disk-oscillation model. By assuming that
a warp has a time-dependent precession, we can well describe observed frequency
correlations among kHz QPOs and LF QPOs in a wide range of frequencies.
