Question

1. The jury is made up of 12 civil people.

2. A jury is composed of 12 common people.

3. There were two juries in the court.

(Are the sentences correct? Do I have to use 'a jury' or 'the jury'? Is #3 correct?)

Answer 1

Not all juries consist of 12 people. So 2) is wrong.

1, and 3 are correct, The use of civil is odd. I am not certain how one determines 12 people are civil, unless you know them an extended time.

Answer 2

For #1, I'd say, "The jury is made up of 12 people." (You don't need the word "civil" in there!!)