Final answer:
The most suitable metric unit used to measure the length of a bicycle would be meters (m) as it is the appropriate size for an object of a bicycle's length.
Step-by-step explanation:
Choosing the Correct Metric Unit of Length
To measure the length of a bicycle, you need to select an appropriate unit from the metric system. The options provided are kilometers (km), meters (m), millimeters (mm), and miles (mi). Kilometers are used for measuring long distances, such as between cities, and therefore are too large for a bicycle.
Miles are not a metric unit and not listed among the options provided for this question. Millimeters, while in the metric system, are too small for such a measurement, typically being used for very small objects. Thus, the most suitable unit for measuring the length of a bicycle would be in meters (m), which are about the size of a yard or an adult's wingspan and fit well for measuring objects of this scale.