Ans.: (b) Aphthous ulcersRef.: Harrison's 19th ed. /239* Apthous ulcers are also called as canker sores/apthous stomatitis and present as round ulcer with yellowish base and surrounded by a red halo.# The usual sites are oral mucosa on the insides of lips , cheeks or below the tongue.# Most of apthous ulcers are <5mm in size and heal within 1-2 weeks.# Painless recurrent apthous ulcers are seen in SLE# Painful recurrent apthous ulcers in oral cavity and genitilia is seen are in Behcet disease