The correct answer is D. Neutrophils. 

The image depicts the palpable purpura of cutaneous small-vessel vasculitis (CSVV), which histologically displays leukocytoclastic vasculitis (LCV). Neutrophils are the cell most responsible for LCV, which underlies the use of anti-neutrophilic agents (e.g. dapsone, colchicine) in the treatment of CSVV.

The remaining cells are not as heavily implicated as neutrophils in the pathogenesis of LCV.

References:PMID: 27787337