Tetragonal crystal system has the following unit cell dimensions:

• A
  $a = b = c$ and $\alpha = \beta = \gamma = 90^\circ$
• B
  $a = b \ne c$ and $\alpha = \beta = \gamma = 90^\circ$
• C
  $a \ne b \ne c$ and $\alpha = \beta = \gamma = 90^\circ$
• D
  $a = b \ne c$ and $\alpha = \beta = 90^\circ, \gamma = 120^\circ$