No resource is perfect. If you are cross-referencing multiple sources, note that early printings of the IF87021 answer key contained a few typographical errors. Specifically:
If you are a teacher or a parent and have lost the original physical key included with the workbook, here are the most effective ways to locate the specific data: Answer Key If87021 Words The Vine
Don't just find the word; use it in a context that proves the root's meaning. No resource is perfect