Silver Iodide Is an Insoluble Salt

Silver iodide is an insoluble salt. If solid sodium iodide and solid silver nitrate are mixed together a reaction to for sodium nitrate and silver iodide occurs but it is extremely slow. However, if the sodium iodide and silver nitrate are first dissolved in water and the two solutions are mixed the reaction occurs very rapidly. Which of the following explain(s) the difference in reaction rates?

A) Ions in solution have high mobility and ions of opposite charges are attracted to each other.
B) The concentration of ions in solution is greater than the concentration of ions in the solid.
C) both of the above
D) neither of the above