x×x×x=3×3×900，

& National Bureau of Statistics; & National Bureau of Statistics; & National Bureau of Statistics; & National Bureau of Statistics; 9x = 00 of 3,

& National Bureau of Statistics; & National Bureau of Statistics; & National Bureau of Statistics; & National Bureau of Statistics; & National Bureau of Statistics; x = 900

Answer: It costs 900 pieces to choose a floor tile with a side length of xdm3.

So choose B.