Which one of the following is present in the chain structure of silicates? 

• A

  ${\left({\mathrm{Si}}_2{\mathrm{O}}_{{ }_5}^{2-}\right)}_{\mathrm{n}}$

• B

  ${\left({\mathrm{SiO}}_{{ }_3}^{2-}\right)}_{\mathrm{n}}$

• C

  ${\left({\mathrm{SiO}}_{{ }_4}^{ }\right)}^{4-}$

• D

  ${\mathrm{Si}}_2{\mathrm{O}}_{{ }_7}^{6-}$