Complex sentence: Environment U.S.A.: 1957--1967 featured the "Who's Who" of pop art. Considered as a summation of the "classical phase" of the American pop art period, the exhibit was curated by William Seitz.
Split into simpler sentences: Environment U.S.A.: 1957--1967 featured the "Who's Who" of the pop art icons. It could be considered as a summation of the "classical phase" of the American pop art period.The exhibit was curated by William Seitz.