I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "The term Iran derives directly from Middle Persian Ērān, first attested in a 3rd-century inscription at Rustam Relief, with the accompanying Parthian inscription using the term Aryān, in reference to Iranians. The Middle Iranian ērān and aryān are oblique plural forms of gentilic ēr- (Middle Persian) and ary- (Parthian), both deriving from Proto-Iranian *arya- (meaning "Aryan," i.e., "of the Iranians"), argued to descend from Proto-Indo-European *ar-yo-, meaning "skillful assembler." In Iranian languages, the gentilic is attested as a self-identifier included in ancient inscriptions and the literature of Avesta,[a] and remains also in other Iranian ethnic names such as Alans (Ossetic: Ир – Ir) and Iron (Ossetic: Ирон – Iron)."? 

What is the term found in an inscription at Rustam Relief that means Iranians?