Choose the statement that is not true. Assume $b \neq 0, c \neq 0$, and $d \neq 0$ as necessary.
$$
\text { (a) } \frac{a c}{b c}=\frac{a}{b} \quad \text { (b) } \frac{a}{b}+\frac{c}{b}=\frac{a+c}{b}
$$
$$
\text { (c) } \frac{a}{b}-\frac{c}{d}=\frac{a d-b c}{b d} \quad \text { (d) } \frac{\frac{a}{b}}{\frac{c}{d}}=\frac{a c}{b d}
$$