Ans. A. Mediastinal shift. (Ref. Sutton radiology 7th ed. 161)Direct signs of lung collapse includeIndirect signs are:i) opacity of the affected lobe(s)ii) crowding of the vessels and bronchi within the collapsed area:iii) displacement or bowing of the fissures.i) compensatory hyperinflation of the normal lung or lobes resulting in an increase in transradiancy with separation of the vascular marking;ii) displacement of the mediastinal structures toward the affected side.iii) displacement of the ipsilateral hilum which changes shape.Special signs of Lung Collapse:1.Rounded atelectasis"Comet tail" sign (vascular shadows seen radiating from opacity). Known in Asbestosis.2.Golden's 'S' signRight hilar/central mass with upper lobe collapse seen as convexity at the medial aspect of pulled up major fissure.3.Broncholobar signLower lobe bronchus is displayed within the opacity of the collapsed left lower lobe.4.Luftsiche! signGerman words luft = air, sichel = sickle, literally describes an 'air crescent' which may be seen between the aortic arch and the medial border of the collapse .The hyperextended superior segment of the ipsilateral lower lobe accounts for the paramediastinal lucency outlining the medial surface of the collapsed right or left upper lobe.