Oscillation of forced neutral differential equations with positive and negative coefficients

Some sufficient conditions are obtained for the oscillation of forced neutral differential equations with positive and negative coefficients [x(t)-R(t)x(t-r)]^'+P(t)x([email protected])-Q(t)x([email protected])=f(t),t>=t"0 where R(t),P(t),Q(t)@?C([t"0,~),R^+),r>0,@t>=0,@s>=0.