Read the following sentence and Identify the function of it in the introduction.<br/> Unfortunately, they do not use circuit simulations to optimize systemdesign and to improve harvester circuit efficiency. ()<br/> A、Explaining the significance or necessity of the research<br/> B、Reviewingthe existing literature relevant to the present study<br/> C、Identifyinga gap in the existing literature<br/> D、Announcing the purpose/focus ofthe study<br/> E、Outlining the paper structure