Task: Question Answering
Input (English): Question: In the presence of a patient with suspected blistering pemphigoid, which of the following tests should we perform to confirm the diagnosis? 
 Options:  <1> Dermatoscopy. <2> Cultivation of the contents of a blister. <3> Skin biopsy for culture. <4> Skin biopsy for histological study and direct immunofluorescence. <5> Analytical with determination of antinuclear and anti DNA antibodies.
Output (English): 4