We have shelter and food.
It should be 3 or 6... Not 100% sure.
Answer;
-Reduce the chance of errors in correspondence
-Easier to use for converting between units while measuring
-Make communication easier between scientists comparing data
Explanation;
-The metric system is a system that is based on joining one of a series of prefixes, including kilo-, hecto-, deka-, deci-, centi-, and milli-, with a base unit of measurement, such as meter, liter, or gram.
-Since the metric system is a decimal system of weights and measures it is easy to convert between units simply by multiplying or dividing by 10, 100, 1000, etc.
-It is an alternative system of measurement used in most countries, as well as in the United States.
It is more of a web because it can start in any order and move into any rock type. example being you can start as a sedimentary rock and turn into a metamorphic rock or igneous rock. a cycle starts anywhere and then goes into a specific cycle.
hope this helps