The parameters of a monoclinic crystal system are .......

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