Phenobarbitone induces liver microsomal enzymes, when taken with warfarin anti-coagulant leads.. Increasing the activity of liver enzymes

Phenobarbitone induces liver microsomal enzymes, when taken with warfarin anti-coagulant leads to:
a- Increasing the activity of liver enzymes.***
So decreases the activity of warfarin.***
b- Increasing the activity of liver enzymes.
So increases the activity of warfarin.
c- Decreasing the activity of liver enzymes.
So increases the activity of warfarin.
d- Decreasing the activity of liver enzymes.
So decreases the activity of warfarin.