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The Buddha describes the diversity of the external elements - 1) the objects of vision, 2) sounds, 3) smells, 4) tastes, 5) physical sensations, and 6) mental objects.
Bāhiradhātunānatta sutta - Diversity Of External Elements
At Sāvatthi.
"Bhikkhus, I will teach you the diversity of elements. Listen to it, pay close attention, and I will speak.
And what, bhikkhus, is the diversity of elements? The objects of vision, sounds, smells, tastes, physical sensations, and mental objects. This is called the diversity of elements.