see sample answer below

a)
subordinate clause: “although some proponents of women’s rights supports the ‘Declaration of Sentiments'”
independent clause: “others considered it too radical.”

b)
subordinate clause: “and public censure”
independent clause: “It was no secret that the work entailed danger”

c)
subordinate clause: “because suffrage is such a previous right”
independent clause: “Americans should vote in all elections”

see sample answer below

independent clauses: “We hold these truths to be self-evident”
subordinate clauses: “that all men and women are created equal” “that they are endowed by their Creator with certain inalienable rights”

see sample answer below

Independent clauses are a good way to show your main idea, while subordinate clauses are good to back up this idea.