In winter, snowmelt pools in fractures and other cavities, then freezes and expands, breaking off chunks of sandstone.


What does cavities mean as it is used in paragraph 4? (NOTE - This is the paragraph that the excerpt was taken out of.)
A.
new small fractures
B.
small colorful patterns
C.
small hidden holes
D.
new colorful lumps

If you could answer I'd appreciate it a lot. Thanks x