The only question that 'the' can answer is, "What determining word tells you that there is only one or a specific one is being referred to?"
It is the first sentence of a paragraph which is the topic sentence.
It in symmetry with sentence a is what? What is a sentence with symmetry in it? This sentence with symmetry is symmetry with sentence this.
Who or what the sentence is about is the subject of the sentence.
Who or what the sentence is about is the subject of the sentence.
The subject of a sentence is who or what that sentence is about.
yes
the meaning of sentence is sentence
A subject in a sentence is who, what, or where the sentence is about.
As a question, it can be a sentence, like: A sentence can have one word, and as a question then it can be a sentence: Who?
compound sentence, simple sentence, and complex sentence
a descriptive sentence is a sentence that describes something in one sentence
This is a sentence. A prisoner has to serve the sentence the judge gives him.