Spanish ships in the late 16th century first brought the potato tuber from South America to Europe whereby in the early 19th century, it had become a reliable backup to cereal crops, particularly in the cold, rain-soaked soils of Ireland. The Irish were soon almost wholly dependent on the potato as their staple food. And they were planting primarily one prodigious variety, the 'Lumper' potato, whose genetic frailty would be cruelly exposed by the fungus 'Phytophthora infestans'. In 1845, spores of the deadly fungus began spreading across the country, destroying nearly all the Lumpers in its path. The resulting famine killed or displaced millions.

41. Which one of the following statements best reflects the critical message of the passage?

• (a) For introducing any foreign plant into a country, the soil and climate conditions of that country should be suitable.
• (b) As a staple food of a country, tuber crops like potato cannot replace cereal crops.
• (c) Some of the fungal infections of plants cannot be prevented or stopped from spreading across large areas.
• (d) Relying on a homogeneous food source is not desirable.