What Purpose Would Sodium Tripolyphosphate Serve in a Detergent Formulation

What purpose would sodium tripolyphosphate serve in a detergent formulation?

A) to aid in removal of rust stains from surfaces and from clothes
B) to improve the flow characteristics of the detergent in the box
C) to aid in keeping the inside of washing machines clean and free from corrosion
D) to complex and hence sequester metal ions in hard water
E) to reduce bacterial growth in the detergent upon storage