The zoologist's argument is that elephants are more motivated to care for members of their herd than for other elephants, based on the observation that elephants spent more time at enclosures containing a distressed calf from their own herd compared to enclosures with a distressed calf from a different herd or an empty enclosure.
To strengthen this argument, we need evidence that the elephants' behavior is specifically driven by a motivation to care for herd members, rather than other factors such as curiosity, general social interest, or external influences.
Option C, if true, would most strengthen the argument:
C. a distressed calf from the elephant’s herd was in the enclosure than when a distressed calf from the elephant’s herd was visible but outside the enclosure
This comparison shows that elephants spend more time at the enclosure only when the distressed calf from their herd is physically accessible (inside the enclosure), rather than when the calf is merely visible but inaccessible (outside). This suggests that the elephants are motivated to be near the calf to provide care or comfort, as proximity would be necessary for such interactions. If the elephants spent similar time regardless of accessibility, it could indicate mere observation or curiosity rather than active care. By demonstrating that accessibility matters specifically for same-herd calves, this option reinforces that the elephants' behavior is driven by a caring motivation tied to herd membership
Why the other options do not strengthen the argument as effectively:
A. they were encouraged by a familiar zookeeper than when they were encouraged by an unfamiliar zookeeper:
This involves an external factor (the zookeeper) and shifts focus to human influence rather than the elephants' intrinsic motivation to care for calves. It does not address herd-based care and could weaken the argument by suggesting that the behavior is influenced by familiarity with humans.
B. the enclosure was empty than when the enclosure contained a distressed calf from a different herd:
This might show that elephants avoid or are less interested in different-herd calves, but it does not directly support the motivation to care for same-herd members. It could indicate general disinterest or aversion rather than a specific care-based motivation for herd members.
D. a distressed calf in the enclosure appeared interested in the approaching elephant than when the calf ignored them:
This focuses on the calf's behavior (interest vs. ignoring) rather than herd membership. If elephants spend more time when calves are responsive, it could suggest social reciprocity or curiosity as the motivation, not necessarily care for distress or herd affiliation. This does not strengthen the herd-based care aspect.
E. a distressed calf from a different herd appeared friendly toward elephants than when a distressed calf from a different herd displayed hostility:
This also emphasizes the calf's behavior (friendliness vs. hostility) and could imply that elephants respond to cues unrelated to herd membership, such as perceived threat or social cues. If elephants spend more time with friendly different-herd calves, it might weaken the argument by showing that non-herd factors can motivate similar behavior.
Hence answer is C