Final answer:
A measurement must include both a unit and the magnitude, which is the numerical part, to properly express a quantity and enable comparison.
Step-by-step explanation:
Any measurement must be paired with two important elements: (a) A unit, which provides a standard for comparison, and (b) the size or magnitude, which is the number in the measurement. When these two components are combined, they express a quantity properly. For instance, a distance may be reported as "5 kilometers," where '5' is the number indicating magnitude and 'kilometers' is the unit signifying the scale of measurement. Without a unit, the number alone would be ambiguous, leaving uncertainty about the actual distance. Therefore, the two elements that must be paired with any measurement are a unit and the size or magnitude expressed as a number.