A county board of elections selects which of the following?

A county board of elections selects the precinct election boards.

Explanation:

The precinct election boards selected by the county boards of elections serve as the smallest units of the entire system of election. Precincts are basically where the voters cast their votes and the board that directly looks after or controls the precinct is called the precinct election board. The term known as a precinct in the US, is referred to as poll elsewhere.

precinct election board