A patient has small, oval multiple ulcers in oral cavity with red erythematous margins. The diagnosis is:

Aphthous ulcer Small and oval multiple ulcers in oral cavity Has red erythematous margins Syphilitic ulcer Firm, painless, non-itchy skin ulceration Tubercular ulcer Firm, nontender erythematous nodules that soften, ulcerate, and form sinuses.