To convert milliliters to liters, you can use the conversion factor that 1 liter equals 1,000 milliliters.
The cylinder holds 6,750 ml. To convert this to liters:
\[ \text{Liters} = \frac{\text{Milliliters}}{1,000} = \frac{6,750 \text{ ml}}{1,000} = 6.75 \text{ L} \]
So, the cylinder holds 6.75 liters.
The correct answer is C) 6.75.