<em>to incorporate general as well as focused information on the topic </em>This is the right answer.
This is important when you write an essay on a topic because a topic is not made up of just general information, or focused information. A topic departs from a general view but then it has to get focalised on one aspect. For example, if we write :" The therapeutic value of animals", this can be a topic. If we write: " Cats help old people to move their wrists. When old people stroke a cat's head, this makes their hand bones move.", this information is focused. We are saying which animal and which therapeutic effect we would like to write about. We have been able to give this focused information because the topic is broad. Besides, we can expand on the topic and talk about the relationship between dogs and blind people.
These options are not right:
-to display the writer’s knowledge of the topic ( In fact, the broad scope of a topic is not related directly to the display of the writer's knowledge, but to the fact the writer should organise the topic coherently).
-to increase the credibility of researched information ( The information will be credible if it is well justified with evidence)
-to make writing on the topic easier ( This has to do with the writer's style and how she will organise her general ideas with her focused ideas).
-to be able to gather information from a variety of sources ( The focus is set on the organisation of the topic and this should reach a broad scope to construct a proper argumentation. The writer can use any number of sources but her argumentation will count more than her sources).
