What is anecdotal evidence? when should it be used (and not used) in a research paper?

What are the most plentiful organisms in an ecosystem

In which type of essay would you expect to find the following passage? during the civil war, the economies of the northern and southern states differed: the north was industrial, while the south was agricultural. while sometimes these interests allowed for mutual economic goals, they also contributed in part to the conflict that fueled the onset of the civil war.

Which sentence demonstrates the most appropriate style for this essay