A common issue in radiocarbon dating is the old wood problem.. This refers to

A common issue in radiocarbon dating is the old wood problem.. This refers to
 
  a. when old wood was scavenged and reused in a later context resulting in a date that does not reflect the time of the activity.
  b. the age of the plant that produced the charcoal must be determined before the radiocarbon date can be calibrated.
  c. only carbon samples from pieces of old wood can be used to procure an accurate date.
  d. that samples taken from old wood must be identified and treated with special chemicals before radiocarbon dating can be performed.
  e. volcanic ashes dating between 500,000 and several million years old.