Final answer:
Washoe, the chimpanzee, demonstrated linguistic productivity by creatively combining signs to represent a swan, an ability that signifies a key aspect of human language.
Step-by-step explanation:
When Washoe, a chimpanzee, combined the signs for water and bird to denote a swan that she saw, she was displaying productivity. Productivity is a linguistic term that refers to the capacity to create and understand new words and sentences. In the case of human language, it is the ability to combine words in an infinite number of ways to generate new meanings or ideas. Animal communication systems, such as the waggle dance of honeybees or the pant-hoots of chimpanzees, often have rules but are typically limited to specific contexts and lack the open-endedness of human language. In contrast, the fact that Washoe formed a new concept by combining known signs demonstrates a creative use of language akin to human productivity.