Final answer:
The units that express volume are cubic meters (m³), cubic centimeters (cm³), and cubic kilometers (km³). These correspond to the volume contained by cubes with sides of those respective lengths.
Step-by-step explanation:
The question Which combination of units expresses volume? pertains to the different metrics used to measure space occupied by an object in three dimensions. The correct answer is none of the options provided directly; volume is expressed as the cube of length units. Therefore, the proper expression of volume would be in units of cubic meters (m³), cubic centimeters (cm³), or cubic kilometers (km³).
In the SI (or metric) system, the base unit for measuring volume is the cubic meter, represented as m³, which is the volume of a cube with edges of exactly one meter in length. Smaller volumes may be expressed in cubic centimeters (cm³), with one cubic centimeter equaling the volume of a cube with 1 cm sides. For even larger volumes, we would use cubic kilometers (km³), each equaling the volume of a cube with sides of one kilometer.
For practical examples, a liter (L) is defined as 1 cubic decimeter (dm³) and is equivalent to 1,000 cubic centimeters (cm³), and one milliliter (mL) is equal to one cubic centimeter (cm³).