instruction:
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?). 
question:
the shale revolution and the gradual shift towards low-carbon sources and renewables.
answer:
background


question:
The effects of two recent crises created by unusual viral infections of the respiratory tract - the severe acute respiratory syndrome ( SARS ) epidemic caused by the novel SARS coronavirus ( 4 , 5 ) and the bird flu ( 6 ) highlight the importance of research into ARDS.
answer:
background


question:
In this paper , we review fully integrated lab-on-chip systems for blood analysis of viral infectious disease.
answer:

purpose