The core concept is understanding synonyms for 'sensitive' in the context of perception. The sentence suggests that humans have a strong ability to notice smells. * **Correct Answer:** B. 'Perceptive' means having or showing a keen ability to notice things, especially subtle things. This aligns with the original meaning of being 'sensitive' to smells. * **Incorrect Options Analysis:** * A. 'Oblivious' means not aware of or not concerned about what is happening around one, which is the opposite of sensitive. * C. 'Indifferent' means having no particular interest or sympathy, which doesn't relate to being sensitive. * D. 'Unaware' means not having knowledge or realizing something, which is a weaker sense of sensitivity and does not indicate a keen ability to notice things. **Key point**: The key is to choose a word that represents a heightened ability to perceive something, which is what 'sensitive' implies in this context. 'Perceptive' does that precisely. **Common Misconception**: Students might confuse 'unaware' with 'not sensitive', but the sentence implies a positive, active sensory ability.