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?). 

Example Input: The gram-negative coccobacillus now designated as Yersinia pestis has been discovered as the causative agent of plague in this Hong Kong outbreak.
Example Output: background

Example Input: A total of 539 NPAs were collected.
Example Output: method

Example Input: we assembled a panel of hepatic and non-hepatic cell lines and assessed their ability to support HCV infection.
Example Output:
method