Gaokao Math Practice Question

6. 记 $S_{n}$ 为等比数列 $\left\{a_{n}\right\}$ 的前 $n$ 项和. 若 $a_{5}-a_{3}=12, a_{6}-a_{4}=24$, 则 $\frac{S_{n}}{a_{n}}=(\quad)$

1. A.$2^{n}-1$
2. B.$2-2^{1-n}$
3. C.$2-2^{n-1}$
4. D.$2^{1-n}-1$