What does SAP SuccessFactors recommend when you create new and custom associations between foundation objects (FO)?

What does SAP SuccessFactors recommend when you create new and custom associations between foundation objects (FO)?
A . All new and custom associations should be built as one-to-many.
B. All new and custom associations should be built between an XML FO and another XML FO.
C. All new and custom associations should be built as one-to-one.
D. All new and custom associations should be built between an MDF FO and another MDF FO.

Answer: D