Which bond is more polar in the following pairs of molecules: $(a)$ $H_3C-H, H_3C-Br$ $(b)$ $H_3C-NH_2, H_3C-OH$ $(c)$ $H_3C-OH, H_3C-SH$

(N/A) $C-Br$ is more polar than $C-H$ because the electronegativity difference between $C$ $(2.5)$ and $Br$ $(2.8)$ is greater than that between $C$ $(2.5)$ and $H$ $(2.1)$.
$(b)$ $C-O$ is more polar than $C-N$ because the electronegativity of $O$ $(3.5)$ is greater than that of $N$ $(3.0)$,leading to a larger dipole moment.
$(c)$ $C-O$ is more polar than $C-S$ because the electronegativity of $O$ $(3.5)$ is significantly higher than that of $S$ $(2.5)$,resulting in a larger electronegativity difference with carbon.