To solve this question, we need to determine the correct word to fill in the blank to make a grammatically correct and meaningful sentence. The sentence given is:
"There is, however, no proof that if we had ___ been working on space."
Let's analyze each option to determine which one fits best:
- not: The word "not" is used to indicate negation. The phrase "if we had not been working" suggests the absence of action or involvement. This fits well within the context of discussing the lack of proof related to working on space.
- occasionally: This implies infrequent action. "If we had occasionally been working on space" suggests some involvement, which contradicts the idea of having no proof.
- seldom: This word means not often or rarely. Similar to "occasionally," using "seldom" implies some action, which is inconsistent with there being "no proof."
- possibly: This word indicates a possibility or potential. "If we had possibly been working on space" weakens the statement, as it introduces uncertainty rather than negation.
Given the context of the sentence, where we're discussing the absence of proof, the correct word to use is not. Thus, the sentence becomes:
"There is, however, no proof that if we had not been working on space."
The use of "not" here clarifies the statement by indicating a hypothetical scenario where no action (working on space) had taken place, aligning with the absence of proof.