relation between absorptivity (a), transmissivity (t) and reflectivity (r)

Question

For an opaque surface, the absorptivity (a), transmissivity (t) and reflectivity (r) are related by the equation:                                                                                                                                         

      (a)  $\alpha +\rho =\tau$                                                            (b) $\alpha +\rho +\tau =0$

      (c) $\alpha +\rho =1$                                                         (d) $\alpha +\rho =0$