Which enzyme is crucial in the conversion of clopidogrel to its active form?
a. Cytochrome P450 3A4 (CYP3A4)
b. Cytochrome P450 2C9 (CYP2C9)
c. Cytochrome P450 2D6 (CYP2D6)
d. Cytochrome P450 1A2 (CYP1A2)