You will be given a definition of a task first, then some input of the task.
In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Article: Little Tom down the street calls our dog "The keep dog".Zip is a sheep dog. But when Tom tries to say" Seep", it comes out "keep". And in a way Tom is right. Zip is always bringing things home for us to keep! I'll tell you about some of them. Zip's first present was a shoe. It was made of green silk. We didn't know how Zip found the shoe. But after a moment Mary, my big sister, told me the shoe had a strange smell. I nodded and held my nose. "What do you think it is?" "It smells like something for cleaning. I think someone tried to clean a spot off the shoe. Then he put it at the door to dry." "Along came Zip. And good-bye shoe!" I said."We should take it back." "We can't ".said my sistter. "Maybe little Tom is right," Mary said. "Maybe Zip is a keep dog!"
Answer: what Zip's first present was made of
Output:
The writer and Mary didn't know _ .