<s>[INST] context: Silhouette sign is some what a misnomer and in the true sense actually denotes the loss of a silhouette, thus, it is sometimes also known as loss of silhouette sign or loss of outline sign 4. The differential attenuation of x-ray photons by two adjacent structures defines the silhouette, e.g. hea borders against the adjacent lung segments, and it is the pathological loss of this differentiation, which the silhouette sign refers to. In sho, it denotes that a mediastinal border can only be obscured by pathology which is in direct anatomical contact. Recognition of this sign is useful in localizing areas of airspace opacities, atelectasis or mass within the lung, with the loss of these normal silhouettes on frontal chest radiographs being generally indicative of the site of pathology . * right paratracheal stripe: right upper lobe * right hea border: right middle lobe or medial right lower lobe * right hemidiaphragm: right lower lobe * aoic knuckle: left upper lobe * left hea border: lingular segments of the left upper lobe * left hemidiaphragm or descending aoa: left lower lobe [/INST] question: Prunning of pulmonary aeries is seen in? | options: A: Right lower lobe B: Right atrium C: Right middle lobe D: Right ventricle | answer: C </s>