Definition: In this task, you will use your knowledge about language (and common sense) to determine what element the marked number refers to. The numbers are marked with two underlines around them, like: _ number _. Your answer should be chosen from the given text, and should not contain other words.
Input: Gilligan:  Hiya , Professor . What are you doing ?
Professor Roy Hinkley: I 'm making notes for a book . It 's to be a chronicle of our adventures on the island ... I think it 's a book people will want to buy , do n't you ?
Gilligan: Sure , I 'll buy _ one _ . I 'm dying to find out what happens to us .

book