  An arguable aspect of the modified gravity theories is that many of them
present the so-called degeneracy problem. For instance, the cosmological
evolution, gravitational collapse and the main features of standard black-hole
configurations, can be mimicked by many of those theories. In this
communication we revise briefly the appropriate observable quantities to be
measured in order to discard alternative theories to LCDM, such as the observed
growth of scalar perturbations with Sloan data and the CMB tensor perturbations
evolution.
