Which of the following pairs has approximately the same ionic size?

• A
  $Zn^{2+}, Hf^{4+}$
• B
  $Fe^{2+}, Ni^{2+}$
• C
  $Zr^{4+}, Ti^{4+}$
• D
  $Zr^{4+}, Hf^{4+}$