Refer to the Scenario Below to Answer the Following Questions

Refer to the scenario below to answer the following questions.
Most people laughed when Evelyn Wong explained her product idea-a solar-powered vacuum cleaner. But the concept was practical and the technology used in the vacuum was the same as that used in many children's toys. After setting up a demonstration booth in a shopping center in Hong Kong, Evelyn felt more assured than ever that her idea would be a hit. Consumers seemed receptive and offered helpful pieces of advice, such as how much they would pay for the vacuum, what colors they would prefer, and why they would not buy the vacuum.
The vacuum itself was dome-shaped, something like a small saucer, with a filter bag on top and sensory nodes along the edges. After being charged in the sunlight, the vacuum could run for 10 hours, covering a floor area of 600 square feet. As the apparatus lightly bumped into table legs, chairs, and so on, the sensory nodes allowed the vacuum to move around the objects in various directions. This is the same type of technology used in the manufacture of children's race cars and walking dolls.
Evelyn knew that the solar-powered vacuum would be especially helpful to both elderly consumers, who may have a more difficult time with vacuuming, and on-the-go consumers who lead busy lives. The price would be above average but would likely reduce after Evelyn recouped some of her costs.
After a 500-unit production run and a substantial financial investment, Evelyn set up a multiple-city test market-in a Hong Kong shopping center and in an appliance store in Shenzhen. "It's such a novel idea," Evelyn added. "People will notice it, even if they don't buy it right away."
-Evelyn's ________ is the practical use of solar power in a vacuum cleaner that is designed to effortlessly sweep the floors of on-the-go and elderly consumers.

A) product idea
B) product concept
C) product image
D) prototype
E) promotional product