In this task, you will be presented with a context from an academic paper and a question separated with a 
. You have to answer the question based on the context.

We compile three Chinese text corpora from online data for three domains, namely, “hotel", “mobile phone (mobile)", and “travel". All texts are about user reviews.  
 Question: What are the sources of the data?

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
User reviews written in Chinese collected online for hotel, mobile phone, and travel domains