Cumulus and stratus clouds belong to which cloud group

Cumulus and stratus are both low level clouds. They are found at a height of about 6500 feet from the ground
Cumulus clouds are the kind of clouds that are woolly and form circles and waves that look like cotton balls . 
Stratus clouds are the ones that sometimes descend to the surface of the ground. These clouds are thin and wispy and not as dense as the cumulus clouds. The colour of both these types of clouds is white.