Answer: Coal is a combustible rock formed by the compression and alteration of thick layers of partially decayed vegetation.
(Coal; is; a combustible rock formed by the compression and alteration of thick layers of partially decayed vegetation) (a combustible rock; formed; by the compression and alteration of thick layers of partially decayed vegetation)
Coal a combustible rock
is formed
a combustible rock formed by the compression and alteration of thick layers of partially decayed vegetation
by the compression and alteration of thick layers of partially decayed vegetation