Your book discusses the memory functioning of patient H.M. who underwent brain surgery to relieve severe epileptic seizures. H.M.'s case has been extremely informative to psychologists by demonstrating that

a. LTM can operate normally while STM is impaired.
b. impairment of one memory system (LTM or STM) necessarily leads to deficits in the functioning of the other.
c. a double dissociation exists for STM and LTM.
d. STM can operate normally while LTM is impaired.

d