单项选择题

Passage Four
Elephants who paint aren’t new. Paintings by Ruby, an Asian elephant who lived at the Phoenix Zoo in Arizona, sold for up to $ 5,000 in the late 1980s, said Dick George, a consultant with the zoo.
"Ruby was about seven months old when she first came to the zoo," said George. "She lived with a goat and some chickens, but she didn’t have an elephant companion for a number of years. She spent a lot of time drawing in the dirt with a stick to make her days more stimulating. Her keeper bought her some art sup- plies." George said, "Ruby was excited about painting right from the beginning."
The elephants at the art academies in the Southeast Asia are taught to hold a paintbrush with the tip of their trunks. Initially, the keeper guides the elephant’s trunk over the canvas(画布) and offers rewards for good performance.
"It only takes a few hours to a day to teach them," said Mia Fineman, an art historian whose book When Elephants Paint is an illustrated history of the Asian Elephant Art and Consrvation Project.

To encourage the elephants to paint well, the keeper （）.

点击查看答案&解析