If a metal has a $fcc$ crystal structure,the coordination number is $12$ because

• A
  Each atom touches four atoms in the layer above it,four in the layer below it,and four in its own layer
• B
  Each atom touches three atoms in the layer above it,three in the layer below it,and six in its own layer
• C
  Each atom touches six atoms in the layer above it,six in the layer below it
• D
  Each atom touches three atoms in the layer above it,three in the layer below it,and three in its layer