Final answer:
To arrange the units millimeter, centimeter, meter, and kilometer from smallest to greatest, the correct order is millimeter (mm), centimeter (cm), meter (m), and kilometer (km). Each subsequent unit is larger than the previous one, with a millimeter being the smallest and a kilometer being the largest.
Step-by-step explanation:
When we arrange the metric units in order from smallest to greatest, we start with the smallest unit which is the millimeter. The order is as follows: millimeter (mm), centimeter (cm), meter (m), and kilometer (km). This is because each unit is a multiple or a fraction of a meter. There are 1000 millimeters in a meter, and a centimeter is one hundredth of a meter. On the other hand, a kilometer is one thousand meters.
To help visualize this, imagine measuring a paperclip. A paperclip is too small to measure in meters or kilometers, which makes millimeters and centimeters the most appropriate choices for such a small object. A centimeter is a manageable unit to measure the length of a paperclip, and you can easily find this measure using a ruler. Meanwhile, a meter is slightly more than 3 feet and is often used in everyday measurements, and a kilometer, being much larger, is used for measuring longer distances like the distance between towns.