In the Reaction of Phosphorus with Chlorine to Form a Phosphorus

In the reaction of phosphorus with chlorine to form a phosphorus chloride, whether PCl₃ or PCl₅ forms depends on ________.

A) which allotropic form of phosphorus is used
B) the amount of chlorine present
C) whether the reaction is carried out in the gas phase or in solution
D) whether the chlorine used is molecular or atomic
E) the amount of moisture present