Final answer:
The standard unit of length in the SI is the meter, which can be further divided into smaller units like centimeters and millimeters for short distances, or expanded into kilometers for longer distances. Miles are used for very long distances.
Step-by-step explanation:
Length is the measurement of the distance between two points, objects, or locations. In the International System of Units (SI), the standard unit of length is the meter (m), which is defined as the distance light in a vacuum travels in 1/299,792,458 of a second. For measuring larger distances, such as the distance around a track, one would typically use kilometers (km), where 1 km equals 1000 meters.
Smaller units of length include the centimeter (cm) and the millimeter (mm), which are more suitable for measuring objects or distances that are closer together. By contrast, for exceptionally long distances like those between cities or geographical locations, the unit of miles is a reasonable choice.