Concept:Converting indirect to direct speech requires preserving the original mood and tense, especially for hypothetical or subjunctive constructions.
Rule / Clue:The indirect sentence uses the subjunctive inversion "were the glacier to retreat" and the conditional modal "could". The reporting verb is "mused" (thoughtful tone). Direct speech must keep the exact inverted structure and modals.
Explanation:The original indirect speech uses a formal hypothetical condition with subject-verb inversion. In direct speech, we quote the exact words, so the inversion remains. The modal "could" is already in the past/conditional form and stays unchanged. The verb "mused" is retained to match the reflective tone.
Option 2 correctly reproduces this: "He mused, 'Were the glacier to retreat another kilometre, the valley ecosystem could irrevocably shift.'"
Option 1 changes to first conditional ("If... retreats"), making the condition more likely and losing the formal tone.
Option 3 uses "said" instead of "mused" and omits essential articles ("the glacier," "the ecosystem"), making it grammatically incomplete.
Option 4 uses "Had... retreated" (third conditional), which changes the meaning to a past impossibility.
Answer:Option B (or Option 2): He mused, "Were the glacier to retreat another kilometre, the valley ecosystem could irrevocably shift."