To convert 6,750 milliliters to liters using the conversion ratio of 1 liter = 1,000 milliliters, you divide the number of milliliters by 1,000:
\[ \text{liters} = \frac{6,750 \text{ milliliters}}{1,000 \text{ milliliters/liter}} = 6.75 \text{ liters} \]
So, the cylinder holds 6.75 liters. The correct response is 6.75.