What is an ambidentate ligand?

• A
  $A$ ligand that attaches to the metal atom through two points.
• B
  $A$ ligand that contains two donor atoms but only one of them can form a coordinate bond at a time.
• C
  $A$ ligand that contains two donor atoms and can form two coordinate bonds simultaneously.
• D
  $A$ ligand that forms a chelate ring.