$A. C_n^k = \frac{n!}{(n-k)!k!}$

$B. A_n^k = \frac{n!}{(n-k)!}$

$C. C_n^k = \frac{n!}{(n-k)!}$

$D. A_n^k = \frac{n!}{(n-k)!k!}$

A.  $C_n^k=\frac{n!}{\left(n-k\right)!k!}$

B.  $A_n^k=\frac{n!}{\left(n-k\right)!}$

C.  $C_n^k=\frac{n!}{\left(n-k\right)!}$

D.  $A_n^k=\frac{n!}{\left(n-k\right)!k!}$

A.  $\frac{n!}{\left(n-k\right)!}$

B. $\frac{n!}{k!}$

C. $\frac{k!}{\left(n-k\right)!}$

D. $\frac{n!}{k!\left(n-k\right)!}$

$A. C_n^k = \frac{n!}{(n-k)!}$

$B. C_n^k = \frac{n!}{k!(n-k)!}$

$C. A_n^k = \frac{n!}{(n-k)!}$

$D. A_n^k = \frac{n!}{k!(n-k)!}$

$A. C_n^k = \frac{n!}{(n-k)!}$

$B. C_n^k = \frac{A_n^k}{k!}$

$C. C_n^k = \frac{A_n^k}{(n-k)!}$

$D. C_n^k = \frac{k!(n-k)!}{n!}$

A. $\frac{\mathrm{k}!\left(\mathrm{n}-\mathrm{k}\right)!}{\mathrm{n}!}$

B.  $\frac{{\mathrm{A}}_{\mathrm{n}}^{\mathrm{k}}}{\left(\mathrm{n}-\mathrm{k}\right)!}$

C.  $\frac{\mathrm{n}!}{\left(\mathrm{n}-\mathrm{k}\right)!}$

D.  $\frac{{\mathrm{A}}_{\mathrm{n}}^{\mathrm{k}}}{\mathrm{k}!}$