Selection principles in function spaces with the compact-open topology

For a Tychonoff space X, we denote by Ck(X) the space of all real-valued continuous functions on X with the compact-open topology. A subset A ? X is said to be sequentially dense in X if every point of X is the limit of a convergent sequence in A. In this paper, the following properties for Ck(X) are considered. S1(S,S)=> Sfin(S,S) => Sfin(S,D) Sfin(D,S) => Sfin(D,D)