What is one of the main uses of levels in surveying?

Answer: B — Setting slope stakes

Levels are primarily used in surveying to determine horizontal and vertical positioning on the construction site. One of the main applications of this tool is setting slope stakes, which involves establishing accurate grades and slopes for construction projects. In highway construction, for instance, levels help in defining the appropriate elevation and incline for roadways, ensuring that water drains properly and that the surface is safe for vehicle operation. By utilizing leveling instruments, surveyors can place stakes at needed intervals to guide construction activities, maintaining the designed slope of the land. Other options mentioned do not align with the fundamental functions of surveying levels. Checking the time of day, measuring temperature, and determining soil types fall outside the purview of focusing on horizontal and vertical angles, thus further clarifying that setting slope stakes is the correct and relevant application of levels in surveying.