Mark states that paper cups are preferable to plastic foam cups because plastic foam cups result in environmentally harmful chlorofluorocarbons and carcinogenic byproducts. Further, foam cups persist indefinitely in the environment.
Tina, however, counters that Mark is ignoring the environmental effects of paper cups. She points to the fact that studies have shown that making paper for the production of paper cups burns more petroleum than foam cups, uses 12 times as much steam, 36 times as much electricity, and twice as much cooling water. Tina also states that because paper cups weigh more, their transportation uses more energy. She also points to the water pollution produced by paper mills and the methane produced by the decomposition of the paper cups.
It's important to note that all of Mark's reasons for his preference of paper cups are ways that the plastic foam cup detriments the environment directly, whereas all of Tina's reasons are indirect ways that paper cups detriment the environment, i.e. through production, transportation and decay. Thus, it's important to decide whether or not we must also take into account a product's indirect impact on the environment in determining the level of its environmental impact, or whether only its direct impact needs to be considered.
This is exactly what answer choice (D) says, i.e. "how much of the chains of causation involved in the production, marketing, and disposal of the products should be considered in analyzing their environmental impact."
Answer choice (A) "how soon each of the kinds of harm cited by Mark and Tina would be likely to be at its maximum level" is not important to decide the issue between Mark and Tina. If the harm of one kind of cup reaches its maximum first, that does not necessarily mean that it's environmental impact was worse. It could just be that its harm manifested more quickly than the other's, so this answer choice is not what is important in determining the issue between Mark and Tina.
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