Different levels of biological organization start from the least complex object and end at the most complex. Every object has objects preceding it that it is made up of.
In this question, the organ system is made up of several organs. A community is made up of several populations of different people. Think about this now: what makes up a population and is made up of organ systems? The most logical answer here according to the flow is B--an organism. An organism is made up of organ systems and makes up a population, which in turn allows several populations to make up a community.
<h3><u>One of the reasons we can't get an accurate count is that the bulk of the things that have yet to be discovered and described are in the realm of the very small: insects, bacteria and other microbes</u></h3>
