If a/b = c/d = e/f , then each of them is equal to = ?

Answer: Option D

$$\begin{array}{rl}& \text{Let,}\\ & \frac{a}{b}=\frac{c}{d}=\frac{e}{f}=\frac{1}{2}\end{array}$$
Now check from option to save your valuable time
$$\begin{array}{rl}& \text{Option D}\\ & \frac{a+3c-5e}{b+3d-5f}\Rightarrow \frac{c}{d}\left[\frac{\frac{a}{c}+3-\frac{5e}{c}}{\frac{b}{d}+3-\frac{5f}{d}}\right]\\ & \Rightarrow \frac{c}{d}=\frac{1}{2}\left(\text{Satisfy}\right)\end{array}$$