NaF is not covalent, but ionic, as Na and F are on opposite sides of the periodic table.
Answer:
D
Explanation: I don't know what the heading is but I think it might be this.
When I was little I cut a hole in my trousers because I didn't like them. I soon regretted this as I was then in a lot of trouble with my parents who had given then to me as a present.
I would go with use direct quotations. Because while the other options will help you to gain a range of research it won't necessarily help to ensure it is accurate. If you use direct quotations you can be sure that your research is accurate as it is from a primary source.
Hope I helped.
