Which statement best describes covalent bases

Answer is: They are often amines.

For example, solution of methylamine (CH₃NH₂) in water.

Balnced chemical reaction:

CH₃NH₂ (aq) + H₂O (l) ⇌ CH₃NH₃⁺ (aq) + OH⁻ (aq).

According to Bronsted-Lowry theory acid are donor of protons and bases are acceptors of protons (the hydrogen cation or H⁺).

Methylamine (CH₃NH₂) is Bronsted base and it can accept proton and become conjugate acid (CH₃NH₃⁺).