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. long-term memory can operate normally while short-term memory is impaired.
b. impairment of one memory system (long-term memory or short-term memory) necessarily leads to deficits in the functioning of the other.
c. most short-term memories can become long-term memories.
d. short-term memory can operate normally while long-term memory is impaired.