Ans. is 'a' ie Auspitz signErythematous scaly lesions on extensor aspect of elbow and knee favours the diagnosis of Psoriasis.The clinical diagnosis of psoriasis can be made by demonstrating Auspitz sign.It is a characteristic finding of psoriasis in which removal of scale leads to pinpoint bleeding.Tzanck testis used in the clinical diagnosis of PemphigusNote that Tzanck smear is used in the diagnosis of herpes virus infection.KOH smearis used for diagnosing fungal infections such as ringworm infections