CR: No Smoke Without Fire – Quickly Eliminate Options

When tackling the GMAT CR, beyond the standard question types like alternative explanations, confusing cause and effect, dynamic equilibrium, understanding a few core logical concepts can really help you zero in on the correct answer. These ideas are especially useful for Explain questions, particularly those that present contradictory information or ask you to explain a surprising outcome.

Practice Question

A popular beach has long had a dolphin feeding program in which fish are given to dolphins several times a day; many dolphins get as much as half of their food each day there. Although dolphins that first benefit from the program as adults are healthy and long-lived, their offspring have a lower life expectancy than offspring of dolphins that feed exclusively in the wild.

Which of the following, if true, most helps to explain the lower life expectancy of offspring of dolphins feeding at the beach compared to other young dolphins?

1. Sharks that prey on dolphins are less common in the open seas off the beach than in many other areas of the open seas where dolphins congregate.
2. Many of the adult dolphins that feed at the beach are females that nurse their offspring there.
3. The fish given to the dolphins at the beach are the same types of fish that dolphins typically catch in the wild.
4. Many dolphins that feed at the beach with their offspring come to the beach only a few times a month.
5. Adult dolphins that feed at the beach spend much less time teaching their offspring how to catch fish in the wild than do other adult dolphins.

Problem-Solving Approach

The core contradiction in this passage is that adult dolphins in the feeding program are healthy and live long lives, but their offspring don’t live as long as offspring of dolphins that forage naturally. We’re looking for the cause of this difference in lifespan between the generations.

According to our “No Wind, No Waves” principle, the explanation must involve a difference or change that affects the offspring but not necessarily the adults. According to the “no wind, no waves” principle, only a “difference” can explain a “difference.”

Initial Screening

Let’s see which options introduce a relevant difference:

• (A) Mentions fewer sharks, which is a difference in the environment, but doesn’t directly link to the offspring’s survival.
• (B) States females nurse their offspring at the beach. This describes a situation, not necessarily a difference that explains the *lower* life expectancy.
• (C) Claims the fish are the same. This explicitly states *no difference* in food, so it can’t explain the observed difference in lifespan.
• (D) Mentions frequency of beach visits. This is a difference in behavior but doesn’t clearly connect to the offspring’s survival.
• (E) Points out a significant difference: adult dolphins at the beach spend *less time teaching* their offspring to hunt compared to other adult dolphins. This is a difference in parental behavior that directly impacts the offspring’s skills.

Options (A) and (E) present differences. Let’s dig deeper.

In-depth Analysis

• Analyzing Option (A): Fewer sharks might mean *adult* dolphins are safer, but it doesn’t explain why *offspring* specifically have a lower life expectancy. Sharks likely prey on dolphins of all ages, so a reduction in sharks wouldn’t selectively harm the young. This option doesn’t bridge the gap between adult health and offspring survival.
• Analyzing Option (E): This option highlights a critical difference in learned behavior. If adult dolphins at the beach spend less time teaching their young essential hunting skills, the offspring are less prepared to survive on their own in the wild. This directly impacts the offspring’s chances of survival, explaining their lower life expectancy, while not necessarily affecting the health or lifespan of the adults who are receiving supplemental food. This fits our “No Wind, No Waves” principle perfectly – a difference in teaching leads to a difference in offspring survival.

Therefore, (E) is the correct answer.

Basic Three Steps for CR

1. Read the passage carefully and pinpoint the contradiction or the surprising outcome.
2. Match these with relevant logical principles (like “no wind, no waves”) to initially eliminate options.
3. Finally, among the remaining options, think deeply about their plausibility and correspondence.

(Next time: We’ll explore the CR concept of “Dynamic Equilibrium.”)