[填空题]
The lowest pressure at xu4wj cxafanm5 gk+4;u85lx: z2dmf/)06j nx9cypn itainable using the best available vacuum techniques is about z/n yicn 96dx)0pmf2j $10^{-12} N/m^2$ At such a pressure, how many molecules are there per $cm^3$ at 0$^{\circ} $C? $\frac{molecules}{cm^3}$