In this task, you are given a sentence from the research paper and your task is to classify the given sentence into the following categories: Background (Why is this problem important? What relevant works have been created before? What is still missing in the previous works? What are the high-level research questions? How might this help other research or researchers?), Purpose (What specific things do the researchers want to do? What specific knowledge do the researchers want to gain? What specific hypothesis do the researchers want to test?), Method (How did the researchers do the work or find what they sought? What are the procedures and steps of the research?), or Finding (What did the researchers find out? Did the proposed methods work? Did the thing behave as the researchers expected?). 
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Question: Background : The potential risks associated with `` toilet plume '' aerosols produced by flush toilets is a subject of continuing study.

Answer: background


Question: rayon-budded swab in a transport tube with a foam 37 pad reservoir soaked with viral transport medium ( Virocult MW950 , Medical Wire & Equipment , 38 Wiltshire , England ).

Answer: method


Question: and crashes happened in Apr 2008 triggered by the Subprime Mortgage Crisis of US.

Answer:
finding