What is central idea that the author develops throughout this essay? what key point support that central idea?

The central idea is the main idea or the most important part of the story.  It can also be an opinion statement that is able to be supported by the details.  As you read the passage, what is is mostly about?  What factual information is presented that can lead you to the main idea.  In other words, the main idea (or central idea) is more general and the supporting details are more focused.  

onto a large boat, and mark the water level that the boat sinks to. then, take the elephant out and put a bunch of marked weights onto the boat until it reaches the same water level. add up the masses of the weights to get the weight of the elephant.

answer: i chose a.

explanation: