Iran is a diverse country, both religiously and ethnically. There are sizable Christian, Jewish, and Zoroastrian minorities, as well as Arabs, Turkmen, and Kurds (among others). Yet the Islamic Republic imposes restrictions on expressions of minority identity. The sale of Christian bibles is an offense, and Muslims who convert to Christianity can be sentenced to death for apostasy. Arabs make up roughly 5% of the population and are concentrated in the restive oil-rich provinces of southwestern Iran. Security forces at times ban Arabs from wearing the keffiyah, a scarf symbol of Arab nationalism, and in November arrested over 80 people attending an Arabic cultural gathering. Though Kurds make up roughly 10 percent of the population, the Kurdish language is also banned from being taught in schools. In 1997, historian Karimullah Tavahodi was jailed for publishing a volume on Kurdish history.