Even in Cases Where Hair Samples Test "Positive" for Substances

Even in cases where hair samples test "positive" for substances of abuse,

A) the hair sample does not accurately indicate when the substance was used.
B) they also identify persons who were only exposed to a chemical, not just those who used it.
C) you must wait 4-6 weeks for the hair to grow long enough to determine whether a person used a compound in the past 24 hours.
D) the rate of hair growth is not variable, but is 1 cm per month.