[tex]\footnotesize \begin{aligned}\sf C_k(n)=\bigg(\frac{n}{k}\bigg)=\frac{n!}{k!(n-k)!} \\ \\ \sf \: n = 5 \\ \sf \: k = 4 \\ \\ \sf \: C_4(5)=\bigg(\frac{5}{4}\bigg)=\frac{5!}{4!(5-4)!} = \frac{5}{1} = 5 \\ \\ \textsf{the number of combination is 5} \\ \\ \boxed{\textsf{Option B}} \end{aligned}[/tex]
