On Thursday, the benchmark Sensex touched 21,000, the first time in three years. However, it couldn't sustain gains, owing to selling of IT shares. Foreign institutional investors net bought shares worth Rs 992 crore, while their domestic peers sold to the tune of Rs 735 crore, according to provisional data. The index declined 42.45 points, or 0.2 per cent, to close at 20,725.43. The Nifty fell 14 points, or 0.23 per cent, to close at 6,164.35. Among blue-chip companies, Reliance Industries declined 1.5 per cent, after gaining as much as 1.6 per cent earlier in the day