Before revision:  It is previously known that unweighted graphshave 2-, 4-, and 6-additive spanners containing (n^{3/2), } (n^{7/5), and O(n^{4/3}) edges, respectively.
After revision:  It is previously known that unweighted graphshave 2-, 4-, and 6-additive spanners containing ), } (n^{7/5), and O(n^{4/3}) edges, respectively.