question: What slowed the development of solar technologies in the early 20th century ?
answer: increasing availability , economy , and utility of coal and petroleum
turker_answer: Increasing availability , economy and utility of coal and petroleum were some of the things that slowed the development of solar technologies in the early 20th century .
rule-based: Increasing availability , economy , and utility of coal and petroleum slowed the development of solar technologies in the early 20th century .