Dear friend, the plural noun 'criteria' comes from Latin, and its singular is 'criterium'. Those latinisms ending in -um generally take -a in the plural. Other examples include 'addendum - addenda', 'curriculum - curricula', etc. Therefore, 'criteria' is used with plural form of verbs - 'criteria ARE'. Some people, nevertheless, prefer singular - 'is' - though this usage should be avoided by care