Final answer:
The best source for researching the impact of ancient Egyptian religious beliefs on temple design is a scholarly study from a reputable institution like Harvard University. The correct answer is option C.
Step-by-step explanation:
The most appropriate source for Donovan to use in his research on the impact of the religious beliefs of ancient Egyptians on the design of their temples would be C. a study by Harvard University on ancient Egyptian religion and temples. This option is likely to be a well-researched and scholarly work, providing more in-depth and reliable information. It falls under the category of secondary sources which are based on the analysis of primary sources such as artifacts, documents, and other materials from the period being studied.