A sentence uses the pronoun 'their' (a possessive adjective) when something belongs to two or more persons or things.
Examples:
The exceptions to using the possessive 'their' is if the gender of the one person is known and if the person or thing is just one.
Examples:
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
A subject in a sentence is who, what, or where the sentence is about.
the meaning of sentence is sentence
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?
This is a sentence. A prisoner has to serve the sentence the judge gives him.
compound sentence, simple sentence, and complex sentence
a descriptive sentence is a sentence that describes something in one sentence