grams
It would be more appropriate to measure 5 math textbooks in grams or kilograms, as they are smaller and more suitable units for measuring the mass of books. Milligrams would be too small a unit for this measurement.
Measure what? Their mass, length, volume?
GRAMS
Metres
Depending on your location, it might be difficult to come up with a meter stick or a tape measure that displays centimeters and meters. It's probably better to measure it in feet and inches and convert it to metric mathematically.
A microgram.
Potatoes are sold by the kilogram.
A thermometer.
distance
Centimeters
kilograms
Neither of those units will produce a very convenient number. But of the two, the kilogram is the better choice.
you would measure it in kilograms