Step 1: Use Speed of Light:
A higher refractive index means light moves slower in the medium, since $n = c/v$. So we can also sort by the speed of light.
Step 2: Rank by Density and Known Data:
A gas like CO$_2$ is very thin, so light goes almost as fast as in vacuum and $n \approx 1$. Water has $n = 1.33$. Crown glass has $n \approx 1.5$. Diamond bends light the most, with $n \approx 2.4$.
Step 3: Write the Sequence:
From smallest $n$ to largest: D (CO$_2$), B (water), A (crown glass), C (diamond).
Step 4: Find the Option:
The sequence D, B, A, C is the third printed option.
Final Answer:
\[\boxed{\text{D, B, A, C (option 3)}}\]