The geometry of the ammonia molecule can be best described as:

• A
  Nitrogen at one vertex of a regular tetrahedron,the other three vertices being occupied by three hydrogens
• B
  Nitrogen at the centre of the tetrahedron,three of the vertices being occupied by three hydrogens
• C
  Nitrogen at the centre of an equilateral triangle,three corners being occupied by three hydrogens
• D
  Nitrogen at the junction of a $T$,three open ends being occupied by three hydrogens