问题
填空题
Since only ______, but not the mind, could be observed directly and objectively, it was the only proper subject of study in psychology.
答案
参考答案：behavior
解析： Since only behavior, but not the mind, could be observed directly and objectively, it was the only proper subject of study in psychology.行为主义心理学认为，只有行为能够被直接并且客观的观察到，而心智则过于抽象，无法描述，因此心理学最适当的研究对象应当是可以观察到的行为。