We present theoretical analysis of the excitation spectra of strongly
interacting Bose-Einstein condenstates based on the correlated basis function
(CBF) theory.  Comparison is made with recent Bragg scattering experiments,
where the strength of the interaction has been varied using the magnetic field.
Large deviations from the mean field approximation are found. We show that a
two-parameter effective interaction potential derived from the fit to the
scattering length and to the theoretical estimate of the effective range is
required, but enough to fit quantitatively the down bending of the line shift
measured in the Bragg scattering for a given scattering length. The frequency
dependence of the dynamic structure function $S(k,\omega)$ for a fixed momentum
evolves with increasing scattering length from a simple narrow distribution
following the Feynman spectrum to a wider structure which has a narrow peak at
the continuum limit.