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Adapted from ZOOM. ZOOM and the ZOOM words and related indicia are trademarks of the WGBH Educational Foundation. ZOOM is produced by WGBH Boston. Funding for ZOOM is provided by the National Science Foundation, the Corporation for Public Broadcasting, the Arthur Vining David Foundations, and public television viewers. This material is based upon work supported by the National Science Foundation under Grant No. 0229796. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.