[单选题]
An object sits on a rotating horizontal diugme(8f z :x,xsc. The disc rot6z/fw rtp i;26 l:ickmates from rest with uniform angular acceleration α. After time t the object slides off l:mwz 2ip6 ;rc ft6/kiof the disc.
What is the linear speed of the object at this time?
A. $αt$
B. $rαt$
C. $\frac{1}{2}αt^2$
D. $\frac{1}{2}rαt^2$
