Is it true that volumes of solids can be expressed in liters or milliliters?

Liters and any denomination of liters are a unit of volume. The definition of matter includes that it has to take up space - volume. So you can indeed use liters and milliliters to measure the volume of a solid. However, the alternative is to use meters (cubed) and any denomination of meters to represent volume. You could say that something is 1.00 liters or you could say that the same thing is 1000 cm3.