(c).

Clustering	Distance of samples
	Criterion: the B value in RGB color space
Categories	I	II	III	IV	V
Number of clustering centers	18	25	14	20	19
Samples in the class	23, 24, 27	2, 10, 21, 22, 28, 31, 32, 34	1, 5	4, 9, 13, 16, 26, 29, 33	3, 6, 7, 8, 11, 12, 15, 17, 30
Scope of feature values	[87,110]	[120,140]	[148,167]	[185,199]	[207,252]
Feature thresholds	B < 120	120 < B < 190			B > 200