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

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

C.  $A_n^k=\frac{n!}{k!}$

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

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

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

C.  $A_n^k=\frac{n!}{k!}$

D.  $A_n^k=\frac{n!}{(n-k)!}$

$A. A_n^k = \frac{n!}{k!}$

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

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

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

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

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

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

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

$A. C_n^k +\hspace{0.17em}{C}_n^{k-1} = C_{n+1}^k$

$B. C_n^k +\hspace{0.17em}{C}_n^{k-1} = C_{n+1}^{k+1}$

$C. A_n^k +\hspace{0.17em}{A}_n^{k-1} = A_{n+1}^k$

$D. A_n^k +\hspace{0.17em}{A}_n^{k-1} = A_{n+1}^{k+1}$

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

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

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

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

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

B.  $C_n^k=\frac{n!}{k!}$

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

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

$A. A_n^k = \frac{n!}{k!}$

$B. A_n^k = n!$

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

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