题目选项分析

Scientist: In an experiment, dogs had access to a handle they could pull to release food into a nearby enclosure that contained a familiar dog and nothing else, contained an unfamiliar dog and nothing else, or was empty. The dogs typically released more food to the familiar dog than to the unfamiliar dog. This suggests that dogs are more motivated to help other dogs they know than to help unfamiliar dogs.

The scientist's argument would be most strengthened if it were true that, in the experiment, the dogs with access to the handle tended to release more food when

【选项】a familiar dog was in the enclosure than when a familiar dog was visible but the enclosure was empty