Which one of the the following usages was a post-Vedic development

(a)

Dharma — Artha — Kama — Moksha

(b)

Brahmana—Kshatriya—Vaishya—Shudra

(c)

Brahmacharya—Grihastashrama— Vanaprastha — Sanyasa

(d)

Indra — Surya — Rudra — Marut