Where is the tangent function sindefined$?$

Choose the correct answer below.

A$.\{\begin{array}{c}x\text{;}x\end{array}$ is an even multiple of $\{$:$\frac{}{2}\}$

A$.(x$:$x$ is an odd multiple of $x)$

c$.\{\begin{array}{c}x\text{:}x\end{array}$ is an odd multiple of $\{$:$\frac{}{2}\}$

D$.$ is an even multiple of $$