instruction:
In this task, you are given a paragraph (from a research paper) and your task is to classify each sentence of the paragraph (assume n sentence) into the following categories: Background, Purpose, Method, Finding/Contribution, or Other. Return the output in this format: 1 - category of sentence 1, 2 - category of sentence 2, ..., n - category of sentence n; where each number indicates the order of the sentence. The categories can be identified using the following questions: 
 Background: - Why is this problem important? - What relevant works have been done before? - What did the previous works miss? - What are the high-level research questions? - How might this help other researchers?
 Purpose: - What specific things do the researchers want to do? - What specific knowledge do the researchers want to know? - What specific hypothesis do the researchers want to test?
 Method: - How did the researchers do it or find it out? - What are the procedures and steps of this research?
 Finding/Contribution: - What did the researchers find out? Did the proposed methods work? - Did things behave as the researchers expected?
Other: put every text fragment that does not fit into any of the categories above here. Put a sentence here if its not in English, is not part of the article, contains numbers and dates, is a caption of a figure or a table, is a formatting error, or you are not sure about it.
question:
Public Health jo urnal homepage: www .e lse vi er.co m/ pu he p u b l i c h e a l t h 1 5 0 ( 2 0 1 7 ) 1 4 9 e1 5 1.
answer:
1 - other, 2 - other


question:
To assess the risk of infectious bacterial aerosols leaking to the environment, the filtration efficiency of a biosafety level 3 (BSL-3) laboratory high-efficiency particulate (HEPA) filter was investigated using the aerosolized bacteria Serratia marcescens. The aerosol size was measured using an Andersen sampler. Eight first stage HEPA filters (numbered 1-8) were distributed in contaminated labs and exhausts from each of the first stage HEPA filters were aggregated and filtered through one second stage HEPA filter before being released to the environment. In total, 8 first-stage and 1 second-stage HEPA filters from the BSL-3 air purification system were analyzed. No S. marcescens was detected in first stage filters 1, 2, 4, 5, 7 and 8 and the second stage HEPA filter. The filtration efficiencies against aerosolized S. marcescens were >99.9999%. First stage filter numbers 3 and 6 had filtration efficiencies of 99.9825% and 99.9906%, respectively. When filter number 3 was replaced by a new filter and the bracket for filter number 6 was sealed, no aerosolized S. marcescens was detected in the filtered air. Our work suggests that the BSL-3 laboratory HEPA filter air purification system is effective against bacterial aerosols, with little to no bacterial leakage into the environment.
answer:
1 - purpose, 2 - method, 3 - method, 4 - method, 5 - method, 6 - finding, 7 - finding, 8 - finding, 9 - finding, 10 - finding, 11 - finding, 12 - finding, 13 - finding, 14 - finding


question:
('filoviruses') that cause severe hemorrhagic fever with human case fatality rates of up to 90%. Filovirus infection requires fusion of the host cell and virus membranes, a process that is mediated by the envelope glycoprotein (GP). GP contains two subunits, the surface subunit (GP1), which is responsible for cell attachment, and the transmembrane subunit (GP2), which catalyzes membrane fusion. The GP2 ectodomain contains two heptad repeat regions, N-terminal and C-terminal (NHR and CHR, respectively) that adopt a six-helix bundle during the fusion process. The refolding of this six-helix bundle provides the thermodynamic driving force to overcome barriers associated with membrane fusion. Here we report the crystal structure of the MARV GP2 core domain in its post-fusion (six-helix bundle) conformation at 1.9 Å resolution. The MARV GP2 core domain backbone conformation is virtually identical to that of EBOV GP2 (reported previously), and consists of a central NHR core trimeric coiled-coil packed against peripheral CHR α-helices and an intervening loop/helix-turn-helix segment. We previously reported that the stability of the MARV GP2 post-fusion structure is highly pH-dependent, with increasing stability at lower pH [Harrison, J.S.; Koellhoffer, J. K.; Chandran, K.; and Lai, J. R. Biochemistry, 2012Biochemistry, , 51, 2515Biochemistry, -2525. We hypothesized that this pH-dependent stability provides a mechanism for conformational control such that the post-fusion six helix bundle is promoted in the environments of appropriately matured endosomes. In this report, a structural rationale for this pH-dependent stability is described, and involves a high-density array of core and surface acidic side chains at the midsection of the structure, termed the 'anion stripe.' In addition, many surface-exposed salt bridges likely contribute to stabilizing the post-fusion structure at low pH. These results provide structural insights into the mechanism of MARV GP2-mediated membrane fusion.
answer:

1 - background, 2 - background, 3 - background, 4 - background, 5 - background, 6 - background, 7 - background, 8 - background, 9 - background, 10 - finding, 11 - finding, 12 - finding, 13 - finding, 14 - finding, 15 - finding, 16 - finding, 17 - finding, 18 - finding, 19 - finding