18. Where in the passage does the author mention a technology that aided in the understanding of double radio sources? (A) Line 2 (B) Line 7 (C) Line 17 (D) Line 21

20. What is the main idea of the passage? (A) There was great demand for the work of eighteenth-century artisans. (B) Skilled sculptors did not exist in the United States in the 1770's. (C) Many foreign sculptors worked in the United States after 1776. (D) American sculptors were hampered by a lack of tools and materials.