It expresses that the people are working together to make a more perfect union and make the United States of America a legitimate country with a constitution. The people in power are chosen by the general population, so it's a form of representative democracy.
If this is a true or false question then it is true.
The correct answer is that it is a dependent clause.
A dependent clause, as the name itself says, depends on a larger clause in order to make sense. As you can see in the example above, that clause is incomplete - it needs to be part of a larger, independent clause in order to get a proper meaning. The other options are all complete sentences, which is something the example is definitely not.
