Choose one of the several options. It is ____ book in our library.

Solution:

• The sentence requires a superlative adjective to describe the book as being the most interesting compared to all others in the library. The options are 'more interesting' (comparative), 'the most interesting' (superlative), 'interesting' (positive), and 'heavy' (a descriptive adjective unrelated to interest level). Therefore, 'the most interesting' fits the context of indicating the highest degree of interest.

Answer: the most interesting