What do you Understand by Avinza, Oramorph SR, MS Contin?

Although morphine (Avinza, Oramorph SR, MS Contin) is well-absorbed when
administered orally (PO), how much of the drug is metabolized on its first pass through
the liver?

a) 90%

b) 70%

c) 50%

d) 30%

e) 10%