sentences:  Production of Audi "S" cars began in 1990 with the S2 Coupé, whilst the first "RS" car appeared four years later with the Audi RS 2 Avant.Today's S and RS models are based on the A/TT/Q models with the same number (e.g.S4/RS 4 is based on the A4 or the TT RS based on the TT), but the "Ur-S4" from 1991 — 1994 was based on the Audi 100/200 later named A6 and the first S2/RS2 generation from 1990 — 1995 was based on the Audi 80/90 platform later replaced by the A4.