Answer: 2. by determining the central idea of each paragraph, 3. by identifying the most important details used to support the central idea of each paragraph, 5. by summarizing the central idea and key details of each paragraph in a single sentence and 6. by finding the common element among the central ideas throughout the text.
Explanation: To trace how an author develops a central idea throughout a text can be very helpful to really understand the structure of a text and even be able to reproduce it when we are writing an essay or any other kind of text. To do it, we need to find the central idea of each paragraph and the details that support that idea, it is very helpful if we condense those two things in one sentence, and finally we find the elements in common about the central ideas in the whole text.