Why Are Two-Component Regulatory Systems Particularly Useful for Controlling Gene

Multiple Choice

Why are two-component regulatory systems particularly useful for controlling gene expression in response to environmental signals?

A) Two proteins controlling a gene means there are two chances to activate a gene.
B) Two proteins delay the response time so the cell can be sure the change is permanent.
C) One of the two proteins can be exposed to the external environment to receive a signal.
D) Phosphorylation is a permanent change so genes are always turned on after signal.