The math question was optional, but every one did it.
The word problem was optional.
Bucket seats are an optional feature on this model.
the homework we had today was optional because we were really good in school today ......but still everyone did it
He could do arithmetic in his head *really fast. *optional
I personally do, but I think it's optional.
Joshua Goschnick and Lachlan Thomas, (By) is optional
He delivered an eloquent speech at the conference, captivating the audience with his articulate words and persuasive arguments.
"Etc" will usually come at the end of a list, so no. I believe that it is optional to put a period after it if it is not at the end of a sentence.
Complex (APEX)
A complete sentence requires a predicate to express an action or state of being. The predicate typically includes a verb or verb phrase and gives information about what the subject is doing or being. Without a predicate, the sentence lacks a complete thought.
If you want complete neutrality, the best sentences are those without subject, verb or object. Punctuation is optional.
The comma typically goes before "but" when it is connecting two independent clauses in a sentence. For example: "I wanted to go to the store, but it started raining."