<prompt> The most common site and type of metaplasia are :Respiratory tract epithelium, Columnar metaplasiaRespiratory tract epithelium, Squeamous metaplasiaEsophagus, Squeamous metaplasiaEsophagus, Columnar metaplasia  <response>: As respiratory tract is exposed to chronic irritation due to dust, Smoke etc, it undergoes squeamous metaplasia , 