Which two types of wells are characterized by small yields and vulnerability to pollution and drought?

The correct choice highlights dug wells and bored wells as types that are characterized by small yields and susceptibility to contamination and drought conditions. Dug wells are typically shallow and constructed by manually digging into the ground, which makes them more susceptible to surface pollutants and fluctuations in groundwater levels during dry spells. Their shallow nature limits the volume of water they can draw, hence their lower yield.

Bored wells, on the other hand, are created using a drilling technique that creates a larger diameter hole than some drilled wells. While they can reach slightly deeper than dug wells, their construction often still results in limited capacity for water storage and increased vulnerability to environmental contaminants due to their proximity to the surface.

In contrast, drilled wells tend to provide much more reliable water supplies due to the depth they can reach and better isolation from surface contaminants. Artesian wells, typically under pressure from aquifers, also do not share the vulnerabilities of both dug and bored wells. Therefore, the characteristics of dug and bored wells distinctly describe their limitation on yield and their higher risk of pollution and drought impact.