The research team was unsure ---- the microbial sample had degraded during transcontinental refrigeration or had been contaminated.
Answer and explanation
Correct answer: A. whether
- Step 1: The presence of alternative coordinates ('or had been contaminated') paired with epistemic uncertainty ('unsure') requires 'whether'.
- Step 2: 'Whether ... or' introduces noun clauses presenting two alternative possibilities.
Answer
whether.
Why not the others: 'That' introduces factual declarative clauses; 'What' is a relative/interrogative pronoun; 'Which' requires definite selection.
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