Step 1: Recall the fact needed:
A few fodder plants make cyanogenic glucosides that release hydrocyanic acid when chewed. Farmers must know which ones, to avoid poisoning cattle.
Step 2: Test the choice numbered 1.
Choice 1 is rice. It is not a normal green fodder and is not linked with cyanide poisoning.
Step 3: Test the choice numbered 2.
Choice 2 is maize. Animals eat it green or as silage without any HCN risk.
Step 4: Test the choice numbered 3.
Choice 3 is Napier. It is a perennial grass fed freely at any stage without HCN danger.
Step 5: Test the choice numbered 4.
Choice 4 is sorghum. It holds dhurrin, which gives off HCN in young plants and in drought, so animals are fed only after maturity. This is the match.
Final Answer:
Sorghum is the green fodder with HCN.
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