Which is the best answer here?

Whether or not we have chosen to use our licenses since then. They remain of enormous value to us.
Which of the following is the best way to write underlined portion of these sentences? If you think the original is the best way. choose option 1.
1. since then. They remain
2. since then, and they remain
3. since then they remain
4. since then; they remain
5. since then, they remain
Please help thanks.
I think is #3 is that correct?

I am far from a grammarian but I would go with #5. However, I'm known as a comma freak; i.e., I'm good at putting in commas to make it sound better. In this case I think it sounds better with a comma AND it is setting off a dependent clause

To determine the best way to write the underlined portion, we need to consider the clarity, coherence, and grammatical accuracy of the sentence.

Let's analyze each option:

1. "since then. They remain"
This option does not use any punctuation to connect the two phrases, which makes the sentence flow awkwardly.

2. "since then, and they remain"
This option adds the word "and" to connect the two phrases, but it is not necessary and makes the sentence slightly redundant.

3. "since then they remain"
This option does not use any punctuation or unnecessary words, making it the most concise and clear choice. Additionally, the subject ("they") is immediately followed by the verb ("remain"), which is grammatically correct.

4. "since then; they remain"
This option uses a semicolon to connect the two phrases. While semicolons can be used to connect related independent clauses, in this case, the phrases are not independent clauses, so it would not be the most appropriate punctuation.

5. "since then, they remain"
This option uses a comma to connect the two phrases, which is a common choice to indicate a pause or separation in the sentence. It is grammatically correct and maintains clarity.

Considering all these factors, options 3 and 5 are both valid choices. Option 3 ("since then they remain") is the most concise, while option 5 ("since then, they remain") provides a slight pause between the two phrases. Ultimately, the choice between them would depend on the desired writing style and preference.