The Main Reason That a Theory Cannot Predict the Effect

The main reason that a theory cannot predict the effect of an increase in the real interest rate on national saving is

A) for borrowers,the substitution and income effects operate in the same direction,but for lenders they operate in the opposite direction.
B) for lenders,the substitution and income effects operate in the same direction,but for borrowers they operate in the opposite direction.
C) for lenders and borrowers,the substitution and income effects operate in the opposite direction.
D) for lenders and borrowers,the substitution and income effects operate in the same direction.