'UnityEngine.Advertisements' not found

Advertisement.Show(); … simply does not work… it was working before but now it stopped… so i made this new project and tried again… with this script

#pragma strict
import UnityEngine.Advertisements;
function Start () {
	 Advertisement.Show();
}

and it gives this error : Namespace ‘UnityEngine.Advertisements’ not found, maybe you forgot to add an assembly reference

services window looks fine too


tried reinstalling unity… still the same… please help ASAP… my games ready to publish

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