Citrus fruit has always been distributed from areas where the fruit is grown to other parts of the country, often by train. In the early 1900s train cars were heated with coal, and it was believed that this heat helped ripen the fruit. Imagine the
surprise of growers and suppliers when fruit that arrived in new boxcars heated by steam arrived unripe. Why did the fruit no longer ripen?
A) The length of time needed to ripen the fruit was met by slow-moving older trains; newer steam-powered locomotives arrived before the fruit ripened.
B) Ethylene, a by-product of coal burning, ripened the fruit in the cars with the coal stove but was absent from the steam-powered trains.
C) The light from the coal-burning stoves caused the fruits to experience short nights, so without this light, they no longer ripened.
D) The steam prevented the buildup of abscisic acid, which is needed to ripen fruit.
Answer: B
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