You are given a sentence and a question in the input. The information provided in the sentence should be enough to answer the question. You're expected to write the correct answer. Do not use any facts other than those provided in the sentence.

Sentence: The city has a rich history, spanning nearly 2000 years, as inferred from inscriptions found in the valley. 
Question: What suggests that Kathmandu is as old as it is?

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Inferences from inscriptions found in the valley.