Answer:
(B) F with a line on top
Explanation:
There is no one single 'correct' way to denote a vector. Most typical is a line over the symbol: [tex]\overline{F}[/tex], or an arrow over the symbol: [tex]\vec F[/tex]. (However, if you want to use your own vector notation, for example, by printing the symbol in bold, then that is fine, too, as long as you clearly define this upfront),
