The correct answer is:
A. interesting.

The sentence would be:
“That is an interesting book. It tells us all about Asia.”

Explanation:
“Interesting” is an adjective used to describe something that captures attention, like a book. The other options do not fit grammatically:
• “Interest” is a noun.
• “Interested” is used to describe someone’s feelings.
• “Best” is a superlative adjective, which is not suitable in this context.