帮我优化以下prompt，
实现更好的上下文的理解:

JavaScript :
var targetLangName = '简体中文';
    var sourceLangName = 'English';    
    
    combined_prompt = 
    `
    You are an expert in the semantic syntax of the ${sourceLangName} language
    and you are teaching me the ${sourceLangName} language.
    I give you a sentence in ${sourceLangName} and a word in that sentence.
    Please help me explain in ${targetLangName} language
    what the word means in the sentence
    and what the sentence itself means.
    
    If you understand, say yes, and then we will begin.`+

    'Yes, I understand. Please give me the sentence and the word.:'+

    `the sentence is: ${user_input_text}\n\nthe word is: ${selected_text_in_textarea}
    `; Please use JSON format in your answer.
user