  We present preliminary results on an experimental study of the nuclear
modification of the longitudinal ($\sigma_L$) and transverse ($\sigma_T$)
structure functions of nucleons bound in nuclear targets. The origin of these
modifications (commonly referred as as the EMC effect) is not fully understood.
Our measurements of R= $\sigma_L / \sigma_T$ for nuclei ($R_A$) and for
deuterium ($R_D$) indicate that nuclear modifications of the structure
functions of bound nucleons are different for the longitudinal and transverse
structure functions, and that contrary to expectation from several theoretical
models, $R_A< R_D$.
