  In this paper we construct combinatorial bases of Feigin-Stoyanovsky's type
subspaces of standard modules for level $k$ affine Lie algebra $C_\ell^{(1)}$.
We prove spanning by using annihilating field $x_\theta (z)^{k+1}$ of standard
modules. In the proof of linear independence we use simple currents and
intertwinining operators whose existence is given by fusion rules.
