An 11-year-old German shepherd mix is presented for evaluation of a subcutaneous mass on its back near the scapula. A smear of material is obtained and stained with a modified Wright's stain. Representative microscopic fields from this sample are shown at 50X and 100X magnification.

What is your diagnosis?

a) Histiocytoma

b) Mast cell tumor

c) Injection reaction

d) Subcutaneous abscess