Which of the following complexes shows six coordination number?

• A

  ${\left[\mathrm{Zn}{\left(\mathrm{CN}\right)}_4\right]}^{2-}$

• B

  ${\left[\mathrm{Cr}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{3+}$

• C

  ${\left[\mathrm{Cu}{\left(\mathrm{CN}\right)}_4\right]}^{2-}$

• D

  ${\left[\mathrm{Ni}{\left({\mathrm{NH}}_3\right)}_4\right]}^{2+}$