B would be the most appropriate. Leaning forward with narrowed eyes fits the definition of scrutinize which is to examine very closely and carefully. Hope it helped :)
B. scrutinize ;
The best synonym for "look" in the sentence is option B: scrutinize, as it accurately conveys Detective Flint's intense and careful observation of what he suspects is a vital clue. The other options do not match the context of critical examination as effectively. This choice aligns with the detective's investigative nature.
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