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: We show that aged mice ( 16-19 months old ) are more resistant to influenza A virus ( IAV ) infection than the young mice.

Answer: finding


Question: We developed a novel concept that allows to considerably improve the performance of conventionally used ÿltering-facepiece respirators against ÿne and ultraÿne aerosols including airborne viral and bacterial agents.

Answer: purpose


Question: the approach constructs a panel of contiguous cDNAs that span the DENV genome and can be systematically and directionally assembled to produce viable , full-length viruses.

Answer:
method