To convert milliliters to liters, you can use the conversion ratio of 1 liter = 1,000 milliliters.
To find out how many liters are in 6,750 milliliters, you can set up the following equation:
\[ \text{liters} = \frac{\text{milliliters}}{1000} \]
Substituting the value:
\[ \text{liters} = \frac{6,750}{1000} = 6.75 \text{ liters} \]
So, the cylinder holds 6.75 liters.
The correct answer is D (6.75).