7. One possible unit of speed is
   a. miles per hour.
   b. kilometers per hour.
   c. light years per century.
   d. all of the above

All of the options are indeed units of speed! Miles per hour (mph) is commonly used in the U.S. and U.K. for road speed limits, while kilometers per hour (km/h) is more common in most other countries. Light years per century is a less conventional unit but is used in astronomy to express the speed of light over vast distances. Each unit has its unique applications, which makes understanding speed quite a fascinating topic!

In practical terms, knowing these units helps in various situations, like driving or calculating travel time for long distances. For instance, if you’re planning a road trip, converting miles per hour to kilometers per hour can help you better anticipate travel times if you are in a country that uses the metric system. Always handy to double-check your unit conversions to avoid confusion—nobody wants to find out they were planning a trip in the wrong unit!