In the following question, choose the pair of words that best fits the blanks to complete the sentence meaningfully.

Although he ________________________ that the ancient manuscript was a forgery, the curators discovered no evidence to substantiate the historian's ______________________ assertion.

Correct Answer: alleged, purported

To complete the sentence meaningfully, let us analyze the context and the meaning of the words needed in both blanks.

Analyzing the sentence structure and context:
1. First blank: "Although he ________________________ that the ancient manuscript was a forgery..."
Here, a verb in the past tense is required to describe what the historian claimed or stated regarding the manuscript being a forgery.
2. Second blank: "...the curators discovered no evidence to substantiate the historian's ______________________ assertion."
Here, an adjective is needed to describe the nature of the historian's claim/assertion, especially given that it is presented without concrete proof or evidence.

Evaluating the options:
• alleged, purported:
- Alleged (verb) means claimed or asserted without proof. Fitting this into the first blank ("Although he alleged that...") makes complete grammatical and contextual sense.
- Purported (adjective) means reputed or claimed to be true, often implies an unproven allegation. Placing this in the second blank ("purported assertion") perfectly matches the context of an unproven claim that curators found no evidence to substantiate.

• angst, hysterical: "angst" is a noun, not a verb required for the first blank.

• frightened, grumpy: Does not fit the logical context of making a historical claim about a manuscript.

• level, believed: "level" does not make sense in the first blank grammatically or contextually.

• referred, fueled: "referred" requires a preposition (e.g., referred to) and does not fit the context.

Therefore, the pair of words that best fits the sentence is alleged, purported.