how DoEs thE Author inDiCAtE onCogEnEs
A．thEy ArE AlwAys in opErAtion in A hEAlthy pErson.
B．thEy rEmAin unhArmFul so long As thEy ArE not ACtivAtED.
C．thEy CAn BE DrivEn out oF normAl CElls.
D．normAl CElls CAn't turn thEm oFF.