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:
focusing on specific applications and limitations of each vaccine category.
answer:
purpose


question:
This paper presents an up-to-date overview and comparison of the analytical performance of sensors and biosensors recently used in clinical analysis.
answer:
purpose


question:
The envelope glycoprotein ( Env ) of the human immunodeficiency virus type 1 ( HIV-1 ) includes the gp120 surface subunit and the gp41 transmembrane subunit.
answer:

finding