1) Explanation

Let's break down the sentence to understand the context and the meaning required for the blank:
- "Although the researcher knew that her claims might be viewed as audacious and would be difficult to corroborate, their $\qquad$ was sufficient to motivate her continued work in the field."
- "Although": This signals a contrast. The claims are "audacious" (bold, daring, perhaps even reckless) and "difficult to corroborate" (hard to prove or confirm). These are negative or challenging aspects.
- "their $\qquad$ was sufficient to motivate her continued work": Despite the difficulties, something about the claims was strong enough to keep her motivated. This "something" must be a positive quality that makes the claims compelling or believable, even if not yet proven.

Therefore, the blank needs words that describe a quality that makes the claims seem true, plausible, or worthy of pursuit, despite their audacious nature and difficulty in corroboration.

Let's evaluate the given options:
- A. adulteration: The action of making something poorer in quality by adding another substance, typically an inferior one. This is a negative term and doesn't fit a motivating factor.
- B. enigma: A person or thing that is mysterious, puzzling, or difficult to understand. While the claims might be puzzling to others, "enigma" itself wouldn't be a primary motivator for continued work in the sense of pursuing their truth.
- C. verisimilitude: The appearance of being true or real. This fits perfectly. If the claims appear true or real, even if difficult to prove, that plausibility could motivate a researcher to keep working on them.
- D. laudability: The quality of being praiseworthy. While the researcher's work might be laudable, the "laudability" of the claims themselves isn't the primary motivator when they are audacious and difficult to prove. The motivation comes from their perceived truthfulness.
- E. erudition: The quality of having or showing great knowledge or learning. This describes the researcher's characteristic, not a quality of the claims.
- F. authenticity: The quality of being authentic or genuine. This is a strong fit. If the claims feel genuine or truly reflect reality, even if hard to prove, that sense of authenticity would motivate continued investigation.

Conclusion:

The sentence implies that despite the challenges, the claims possessed an intrinsic quality that made them seem true or genuine, thus driving the researcher's continued efforts. Both "verisimilitude" (appearance of truth) and "authenticity" (genuineness, realness) capture this motivating quality.

The final answer is $\(\mathrm{C}, \mathrm{F}\)$.