Mercury Ions (Hg²⁺)are Very Difficult to Dissolve in a Solution

Mercury ions (Hg²⁺) are very difficult to dissolve in a solution of water, or even a dilute solution of NaOH. But if ammonia is added to the water, mercury ions are more readily soluble. Which of the following best explains why this happens?

A) Mercury ions form complex ions with ammonia in solution, which aids the solution process.
B) Ammonia causes the mercury ions to become oxidized.
C) Ammonia causes the mercury ions to lose their charge.
D) Mercury is more soluble in a basic solution than in a neutral solution.
E) This process is still not fully understood by chemist.