[A]
The formal charge becomes one unit more positive at the starting atom and one unit more negative at the terminal atom
[B]
The last arrow in a chain must be either a bond making arrow terminating at a sextet atom, or a bond breaking arrow.
[C]
When a bond is broken, this is represented by a curved arrow pointing towards from the bond from which electron will be transfered and ending the arrow pointing away towards the next unoccupied molecular orbital
[D]
Curly arrows are superimposed over the structural formulae of reactants in a chemical equation to show the reaction mechanism