SAT Question af4300b0: Words In Context answer and explanation

English - Words In Context - Fill In Blank Multi Word Phrase
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The creation of Lotte Reiniger’s 1926 animated film The Adventures of Prince Achmed was ______ process. Over the course of three years, Reiniger and her collaborators painstakingly made more than 250,000 individual images of hand-cut paper silhouettes and repeatedly had to invent entirely new methods and tools to create the special effects Reiniger envisioned.
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Difficulty:Hard
Which choice completes the text with the most logical and precise word or phrase?