Which of the following topics is too narrow for an explanatory essay? how to make homemade bread. selecting a type of yeast to make homemade bread. methods of breadmaking from colonial america. using trial and error to find the best oven temperature to bake bread.

I believe it is "using trial and error to find the best oven temperature to bake bread" is the most narrow topic for an explanatory essay.

Since explanatory writing tends to deliver information, method of trial and error is not such a thing, it is the process of making repeated trials or tests, improving the methods used in the light of errors made, until the right result is found. (according to Collins dictionary)

Just look in both of the stories and write a part from each story.