Answer: B) So they can communicate their results without confusion
Explanation: There are other systems besides the metric system, though the metric is the most commonly used system. In the SI international system, all units are derived from each other, forming a unique international standard. That way, all scientists around the world, or at least most of them using the SI system, can communicate in a unique scientific "language" without confusion and misunderstanding.
This is an example of exchange theory.
In sociology, exchange theory has to do with maximizing benefits while also minimizing costs. When applied to Bill and Cathy's situation, they are taking advantage of each other's skills in order to minimize costs - Bill can cook and Cathy can't (so they can prepare food on their own) and Cathy can repair stuff and Bill can't (so they don't have to get a handyman).
Bacteria and cyanobacteria is the best bet
