This is a classic toxicology matching item. The signature clue most strongly tied to a poison is the bitter-almond smell of cyanide, which is the intended single best (circled) response.
Cyanide blocks cytochrome c oxidase, producing histotoxic hypoxia; cells cannot use oxygen, so venous blood stays bright red and the breath/tissues carry a bitter-almond odour.
For completeness, the remaining associations are also genuine: carbon monoxide forms carboxyhaemoglobin causing cherry-red lividity; phosphorus (along with arsenic and thallium) gives a garlic-like odour and luminous, "smoking" stools; organophosphates inhibit acetylcholinesterase, flooding the body with acetylcholine and causing copious secretions (lacrimation, salivation, bronchorrhoea) summarised by SLUDGE/DUMBELS.
Among these, the cyanide-almond link is the most distinctive and exam-tested pairing.
\[\boxed{\text{Cyanide} \rightarrow \text{bitter almond smell}}\]