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?). 

Q: The sensitivity of EM increased 25 % after virus concentration by ultracentrifugation.

A: method
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Q: Silver nanomaterials ( Ag NMs ) have attracted great interests in recent years due to their excellent anti-microorganism properties.

A: background
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Q: In the present report we have compared the CNS lesions induced by JHMV in lethally infected and T cell clone protected mice.

A:
purpose
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