Regarding implicit and explicit memory, which of the following statements is TRUE?

Regarding implicit and explicit memory, which of the following statements is TRUE?
 
  a. Implicit memory requires a conscious effort to recall, while explicit memory does not.
  b. Explicit memory requires a conscious effort to recall, while implicit memory does not.
  c. Both implicit and explicit memory require a conscious effort to recall.
  d. Neither implicit nor explicit memory requires a conscious effort to recall.
  e. Implicit memory requires a conscious effort to recall, while explicit memory does not, but only for procedural memories.