Here is the general process you should use for EXPLAIN DISCREPANCY problems:
1. Evaluate the given circumstance / phenomenon.
2. Think about what you would have expected / what the normal outcome would likely have been (this is usually unstated).
3. Think about why that's at odds with the actual surprising outcome in this case.
4. Try to think of what information might be missing (not always easy to anticipate; sometimes you won't know until you get to the answers).
5. Select an answer that keeps both the given circumstance and the surprising outcome true.

Common wrong answer types:
- explain the given, but don't connect it to the surprising outcome
- support the expected outcome rather than the surprising one
- equally justify the expected and the surprise (the "no-impact" scenario)

Let's break down this problem:

Given: a) dolphins get half their food from the feeding program, b) adults are healthy and long-lived
Expected outcome: you'd think their offspring would also be healthy and long-lived
Surprising outcome: but in fact, offspring have a lower life expectancy

We need to pick an answer that keeps true both that adults are healthy and that their offspring have a lower life expectancy.

Let's look at the answer choices...

A. 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.
This would lead us to believe that all the dolphins - adults and offspring - would live longer.

B. Many of the adult dolphins that feed at the beach are females that nurse their offspring there.
Again, you'd think that this would help the offspring, because they're being nursed close to a food source.

C. The fish given to the dolphins at the beach are the same types of fish that dolphins typically catch in the wild.
This adds no information about why offspring are worse off.

D. Many dolphins that feed at the beach with their offspring come to the beach only a few times a month.
If they come with their offspring, then why aren't adults and offspring both healthy? This doesn't add any distinguishing details.

E. 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.
Yes! If adults aren't teaching their offspring to hunt, then the offspring will be worse off than the offspring of dolphins who don't get fed.

The answer is E.