The correct answer is C and D.
C. County.
D. State.
County and State are some of the types of conventions which came into being in 1830.
Convention is termed as a gathering of people who meet in time in order and in an arranged place to engage in common interest.
Some conventions include trade conventions, fandom conventions, profession and industry conventions.
The United States convention can call for constitution convention. Different states which are sovereign beside their permanent legislature they call for conventions.