To determine the stereochemistry of the malic acid formed by the hydration of fumaric acid, we must consider the mechanism of addition and the configuration it results in.

Fumaric acid is a trans isomer, and during the hydration, water adds to the double bond. The addition of water can occur from either the "A face" or the "B face" of the double bond.

1. Concept of Stereochemistry:
   • The addition of groups to a double bond can create chiral centers, resulting in stereoisomers.
   • In this case, the center becomes chiral after the addition of water, and the configuration (R or S) depends on the direction of the addition.
2. Addition from the A Face:
   • When water adds from the "A face," the orientation of the groups is such that the order of substituents around the chiral center aligns with the S configuration.
3. Other Options:
   • Adding from the "B face" doesn't result in the S isomer; it would actually give a different stereochemical outcome.
   • The statement about a racemic mixture isn't correct in the case of specific face addition because each face leads to a specific stereoisomer.

Conclusion: The correct statement is that addition specifically from the A face gives the S isomer of malic acid.