Read the following sentence and Identify the function of it in the introduction.
Therefore, the aim of this paper is to present an improvement of theprevious calculation tool under the overcast conditions and to offera new analytic formula for the pipe’s optical efficiency whichprovides better results than the obviously used standard CIE formula.()
A、Explaining the significance or necessity of the research
B、Reviewingthe existing literature relevant to the present study
C、Identifyinga gap in the existing literature
D、Announcing the purpose/focus ofthe study
E、Outlining the paper structure