Which of the following is considered a conditional use that may be allowed on a case-by-case basis?

In the context of zoning regulations, a conditional use is typically a use that, while not permitted by right under the zoning ordinance, may be allowed under specific conditions and with the proper permitting process. This process often involves a review by a planning board or zoning commission to determine if the use will have an adverse impact on the surrounding neighborhood or environment, and what conditions might mitigate those impacts.

Farming is generally considered a permitted use in many zoning classifications, particularly in agricultural or rural areas, and does not typically require a conditional use permit. Public parking is often accounted for within the zoning regulations as a necessary aspect of commercial and public space usage and would similarly be classified as a permitted use rather than a conditional use. Junk yards, on the other hand, are sometimes categorized under conditional uses due to their potential negative impacts on the environment and community aesthetics, but this can depend heavily on local laws and regulations.

Given this understanding, it is clear why the answer suggesting none of the given options constitutes a conditional use is appropriate—it highlights the difference between permitted uses and conditional uses in the realm of zoning laws. Conditional uses are those specifically evaluated for their impacts, while the listed items do not uniformly fit this designation.