The correct answer is 3. It’s the rhythm and flow of the language, aided by a strong structure.
Step-by-step explanation:
In texts, including academical and non-academic ones the word flow refers to the connection between sentences and paragraphs, the transition between ideas and in general terms the structure of a text that makes all its part to be linked to each other and create a strong structure that has a flow or rhythm while being read, which means the reader goes from one idea or section to the other without feeling an important break or disturbance and the connection of all these elements contribute to the development of the main point or idea. Therefore, according to the previous ideas, the statement that best describes fluency is " It’s the rhythm and flow of the language, aided by a strong structure" as fluency refers to the rhythm and flow in a text but also to the strong and connected structure a text has.