Final answer:
The sentence correctly using a signal phrase and quoting the source is "Ornithologist Lee Sparks describes Harpy Eagles as birds that have 'a majestic and enchanting appearance but are insanely dangerous predators.'"
Step-by-step explanation:
The sentence that best uses a signal phrase to credit the information from the source about Harpy Eagles is: "Ornithologist Lee Sparks describes Harpy Eagles as birds that have 'a majestic and enchanting appearance but are insanely dangerous predators.'" This sentence properly attributes Lee Sparks as an expert in the field of ornithology and also uses quotation marks to indicate the precise phrasing taken from the original source material. Further, it maintains the credibility and authority of the source by mentioning Lee Sparks' professional title.