How many of the following are thiospecies (containing S-S bonds)
${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_2,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_3,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_4,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_5,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_6,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8,{\mathrm{S}}_3{\mathrm{O}}_9$

$$\begin{gathered} {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_2:\mathrm{Thiosulphurous} \mathrm{acid} \\ {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_3: \mathrm{Thiosulphuric} \mathrm{acid} \\ {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_4: \mathrm{Dithionous} \mathrm{acid} \\ {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_5: \mathrm{Pyrosulphurousacid} \\ {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_6: \mathrm{Dithionic} \mathrm{acid} \\ {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7: \mathrm{Pyrosulphuricacid} \\ {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8: \mathrm{Peroxydisulfuric} \mathrm{acid} \\ {\mathrm{S}}_3{\mathrm{O}}_9: \mathrm{trimer} \mathrm{of} \mathrm{sulphur} \mathrm{trioxide} \end{gathered}$$