In general, operons that encode the enzymes of a biosynthetic (anabolic) pathway (such as the trp operon) are _____, and those encoding the enzymes of a catabolic pathway (such as the lac operon) are ___.
a.repressible; inducible
b.inducible; repressible
c.permanently on ; permanently off
d.permanently off; permanently on
e.easily mutated; resistant to mutations