Answer:
c) Trigonal pyramidal
Step-by-step explanation:
Since NH₃ contains a nitrogen atom bonded to 3 hydrogen atoms with a lone pair, its molecular geometry is trigonal pyramidal. If it weren't for the lone pair, its molecular geometry would be trigonal planar, but with the lone pair there is more repulsion between the electrons (because they have negative charges. Remember: opposites attract), so the bonds are pushed down into a more pyramidal shape.
Remember, its electron domain geometry is tetrahedral, because the electrons are located in 4 different features of the molecule: the 3 bonds and the 1 lone pair.