A disc has a radius of 5 cm. If the disc rotates about its central axis at an angular speed of 8 rev/s, what is the linear speed of a point on the rim of the disc?  $\textasciitilde$  $\textasciitilde$ 
选项为:A:0.4m/s  B:2.5m/s  C:3.9m/s  D:50m/s  请回答其中一个选项.