Here's why:

* Structure: Ammonia has a central nitrogen atom bonded to three hydrogen atoms.

* Sigma Bonds: Sigma bonds are the strongest type of covalent bond and are formed by the direct overlap of atomic orbitals.

* Hybridization: Nitrogen in ammonia undergoes sp³ hybridization, meaning it has four hybrid orbitals. Three of these hybrid orbitals form sigma bonds with the three hydrogen atoms.

* Lone Pair: The remaining sp³ hybrid orbital holds a lone pair of electrons, which is responsible for ammonia's basic properties.

Therefore, ammonia has three sigma bonds, each between the nitrogen atom and one of the hydrogen atoms.