Which of the following molecules contain polar covalent bonds?
$$
\begin{array}{l}{\text { a. sulfur, } \mathrm{S}_{8}} \\ {\text { b. fluorine, } \mathrm{F}_{2}} \\ {\text { c. iodine monochloride, ICl }} \\ {\text { d. hydrogen bromide, HBr }}\end{array}
$$