What is the lowest type of cloud?

The correct answer is stratus, which is indeed the lowest type of cloud. Stratus clouds typically form in low, horizontal layers and can cover the entire sky, resulting in overcast conditions. Their base is generally found at very low altitudes, usually below 6,500 feet, and they often bring light rain or drizzle.

In contrast, cumulus clouds, while also low-level clouds, tend to have a more vertical development and are often associated with fair weather. Cirrus clouds are high-altitude clouds, thin and wispy, formed at heights above 20,000 feet and are not considered low-level clouds. Nimbus refers to a type of cloud associated with precipitation and can occur at various altitudes, depending on the cloud formation. Therefore, stratus correctly identifies the lowest type of cloud among the options provided.