Inches.
miles or kilomiters
In most countries, it is customary to measure that in liters.
Cm
pounds
The basic metric unit for length is the metre. Rivers would be measure in kilometres (1,000s of metres)
Probably Centimeters
Inches.
inches in customary units
miles or kilomiters
well if you have a small river less than a mile long you will probably want something like a kilometer or meter. But if it is a longer river you may want to use miles or kilometers (the metric system is shorter but easier to convert.)
The width of a river will generally be measured in feet or meters, depending on if you use Imperial or Metric.
The answer depends on which characteristic you wish to measure: its diameter, volume, mass, weight, etc.
It depends on what you want to measure. Their mass or size?
Seconds
In most countries, it is customary to measure that in liters.
You would typically use fluid ounces (oz) or cups (c) to measure the volume of a mayo jar in customary units.