In general,
[tex]\begin{gathered} \frac{w}{x}*\frac{y}{z}=\frac{w*y}{x*z} \\ x,z\ne0 \end{gathered}[/tex]
Therefore, in our case, (Notice that since A/B and C/D are rational expressions, B and D cannot be equal to zero)
[tex]\frac{A}{B}*\frac{C}{D}=\frac{A*C}{B*D}[/tex]
Notice that the left side of each option includes the term
[tex]\frac{A}{B}*\frac{D}{C}[/tex]
However, we cannot assure that C is different than zero because it is only stated that C/D is rational.
Furthermore,
[tex]\frac{A}{B}*\frac{D}{C}=\frac{A*D}{B*C}[/tex]
And (A*D)/(B*C) is not included among the options.
Therefore, the answer has to be option D as it is the only one that correctly expresses the multiplication of two fractions.
Remember that there is a mistake in each option, the left side has to be A/B*D/C
