What does it mean for a synthetic circuit to interface with natural cellular processes?

A) Natural genes can be used as a foundation for design of synthetic circuits.
B) Complete synthetic genomes are transplanted into natural cells.
C) Small fragments of synthetic DNA are incorporated into living cells.
D) The output of a synthetic circuit is controlled by an endogenous signal.
E) Natural metabolic pathways can beengineered by site-directed mutagenesis.