Which of the Following Statements Is TRUE of Small Effector

Which of the following statements is TRUE of small effector molecules?

A) Small effector molecules cause a conformational change in a regulatory protein.
B) Small effector molecules can prevent a repressor from binding a gene region.
C) Small effector molecules regulate gene transcription.
D) Small effector molecules regulate gene transcription by binding a regulatory protein.
E) All of the choices are correct.