Given the task definition and input, reply with output. 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.

Background: Respiratory protection effi ciency of facemasks is critically important in the battle against communicable respiratory infections such as infl uenza and severe acute respiratory syndrome (SARS). We studied the spatial distributions of simulated virus-laden respiratory droplets when human subjects wore facemasks and were exposed to regulatory viral droplets by conducting in vivo experiments in facemask use. Methods: Transmission pathway of aerosols of Fluorescein-KCl solution through facemasks and protective effi ciency of facemasks were examined by using normal surgical facemasks and two facemasks with exhaust valves (Facemask A) and exhaust holes (Facemask B) covered with the same surgical fi lters situated at the back of the facemasks. Fluorescein-KCl solution was sprayed onto the faces of participants wearing the facemasks and performing intermittent exercises on a treadmill in a climatic chamber. Results: Experimental results showed that when droplets spread onto a person face-to-face over short distances, 92.3% to 99.5% of droplets were blocked by the front surface of the facemask, whereas only 0.5% to 7.7% of droplets reached the back of the facemask. Both facemasks A and B had near or over 99% protection effi ciency, compared with that of 95.5% to 97% of surgical facemasks. Using the same fi lters as normal surgical masks, facemasks A and B provided more effective respiratory protection against communicable respiratory infections such as infl uenza and SARS by the location of the breathing pathway to the back of the facemasks. Conclusions: Separating the breathing pathway from the virus-contaminated area in facemasks can provide more effective protection against communicable respiratory infections such as infl uenza and SARS.
1 - background, 2 - purpose, 3 - method, 4 - method, 5 - finding, 6 - finding, 7 - finding, 8 - finding, 9 - finding, 10 - finding, 11 - finding, 12 - finding