You can invent any number of nonstandard units, but none of them is "best". It is best to use standard units, that is, the meter.
4-5 1/2 meters
Whole numbers are the best representation of students.
Measurement error: obviously!
metres would be the best way to work out the length of a classroom as centimetres are to small and kilometres are far to large
Yard
Answer: meters
200mm
The best measurement for a phonebook would be its dimensions, typically expressed in height, width, and thickness. This provides a clear understanding of the physical size of the phonebook.
milimeters
A millimetre.
9 cm
You can invent any number of nonstandard units, but none of them is "best". It is best to use standard units, that is, the meter.
It's Yard
in miles
The metric measurement that is the best estimate for the length of a car is typically in meters or centimeters. This allows for a more precise measurement compared to using larger units such as kilometers.
Inches or centimeters.