Explanation:

- The passage discusses the resilience of the soya bean plant.

- It describes the conditions under which the plant can thrive.

- Option 1: unfavourable indicates that the plant can withstand difficult or adverse conditions.

- Option 2: injurious suggests harmful conditions, which is less commonly used in this context.

- Option 3: favourable denotes good conditions, but this does not align with the narrative of resilience.

- Option 4: agreeable refers to pleasant conditions, which does not suit the context of enduring hardship.

- The passage highlights the strength of the soya bean to withstand challenging environments, making "unfavourable" the most appropriate choice.

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