An economist conducts a "natural experiment" by （ ）

A、choosingtwogroupsofpeople—acontrolgroupandatestgroup—andprovidingspecialtreatmentforthetestgroup.
B、usinganimalbehaviortomakeinferencesabouthumanbehavior.
C、usinghisorherownintuitiontosurmisewhatpeoplewilldoinagivensituation.
D、pollingothereconomiststoseeiftheybelieveatheory.
E、takingreal-worlddataasitisgiven,andusingittotestatheory.