Which of the following conditions will lead to a cloud base being lower?

The condition that leads to a lower cloud base is increased humidity. When the atmosphere contains more moisture, it becomes easier for air to reach saturation. When air rises, it cools, and with higher humidity levels, it can reach the dew point more quickly. This results in condensation and the formation of clouds at lower altitudes. Higher humidity means there's more water vapor present, facilitating cloud formation closer to the ground.

In contrast, high pressure typically leads to clear, stable air conditions with less vertical development of clouds, thus contributing to a higher cloud base. Low moisture content means that there is insufficient moisture in the air to form clouds, which would also lead to a higher cloud base. Higher temperatures generally increase the capacity of air to hold moisture, which might delay saturation and cloud formation, again resulting in a higher cloud base. Increased humidity is the primary factor that causes clouds to form at lower altitudes.