A middle-aged man developed multiple flat ulcers in his palate, tongue, and buccal mucosa. The lesions measured approximately 1 cm in diameter and were preceded briefly by bullae. The le-sions have been persistent for 6 weeks. He has no skin, eye, or genital lesions. Biopsy shows acantholysis with intraepithelial separation. He most likely has:

a. Erythema multiforme
b. Discoid lupus erythematosus
c. Primary herpes simplex infection
d. Mucous membrane pemphigoid
e. None of the above

E