Which of the following statements about retinoic acid and its derivatives is false?

Select one:

a. A deficit of vitamin A can lead to fetal abnormalities.b. An excess of vitamin A can lead to fetal abnormalities.c. Retinoic acid acts by binding to key DNA sequences, resulting in the expression of faulty mRNA molecules.d. Retinoic acid acts as a roofplate signaling molecule.