where f_{1},
f_{2}: R  > R, and g_{1}, g_{2}: R^{2}  > R are continuous
functions, R
= (∞, +∞), τ_{j}(t) 0, j = 1,2, ... m
are bounded continuous functions on R,
and p(t) is a bounded continuous function on R^{+ }= [0,+∞).
We obtain some new sufficient conditions for all solutions and their
derivatives to be bounded, which substantially extend and improve important
results in the literature.
