Which of the following statements about Therapeutic Drug Monitoring are correct?

Which of the following statements about therapeutic drug monitoring are correct?
1 ❏ TDM is especially useful for drugs with a narrow therapeutic index
2 ❏ Plasma concentration always directly reflects drug efficacy
3 ❏ TDM helps in adjusting dosage for individual patient needs

Choose:
A ❏ if 1, 2, and 3 are correct
B ❏ if 1 and 2 only are correct
C ❏ if 2 and 3 only are correct
D ❏ if 1 only is correct
E ❏ if 3 only is correct