A microgram.
kilometre
Tonnes
It would be millimetres.
Kilometers
You would use meters. Or, if the trail is more than 1000 meters, you can use killometers
You would use the metric unit "liters" to measure the capacity of a hot water tank.
Metres
You would use kilograms (kg) to measure someone's mass in metric units.
You would typically use the metric unit of centimeters to measure the growth of your hair.
You would use liters (L) to measure the volume of a soda container in the metric system.
You would use the metric unit "kilograms" to measure the weight of a bag of groceries.
A microgram.
Potatoes are sold by the kilogram.
A thermometer.
distance
kilograms