Which of the following statements about shielding is false?

a. shielding is a decreased effect of the external magnetic field due to the induced magnetic field in the molecule.
b. deshielding shifts the signal or peak downfield shielding is an increased effect of the external magnetic field due to the induced magnetic field in the molecule.
c. the standard reference for measuring shielding effects is TMS.
d. shielding determines the chemical shift of the atom.