1. Understanding the Context:
- The sentence acknowledges that the physicist's work has "some innovative notions" but states we cannot characterize it as $\qquad$ .
- The blank should contrast with "innovative notions," meaning we're looking for words that describe work that is NOT innovative or groundbreaking.
2. Analyzing the Options:
B. novel (Correct): Means new or original. The phrase "hardly characterize as novel" implies the work isn't truly innovative despite having some new ideas.
C. pioneering ( $\downarrow$ Correct): Means groundbreaking or leading. Saying it's "hardly pioneering" suggests it's not as revolutionary as it might seem.
A. conventional and D. commonplace: These would imply the work is ordinary, but the sentence structure suggests we're judging its innovativeness, not its commonness.
E. frivolous: Means silly or trivial - irrelevant to the context.
F. unoriginal: While this could fit, it's redundant with "hardly novel/pioneering" and less precise.
3. Why These Two Words Work Best:
- Both "novel" and "pioneering" directly address the level of innovation, which is the focus of the contrast with "some innovative notions."
- They create the nuanced meaning that while there are some new ideas, the work overall isn't truly groundbreaking.
4. GRE Relevance:
- This question tests vocabulary precision (novel vs. conventional) and the ability to recognize degrees of meaning.
- The dual correct answers reflect the GRE's tendency to accept multiple valid interpretations when justified.

Final Answer: B. novel and C. pioneering