[单选题]
An object sits on a rotating(-zy2 ;a w6q7ic1gwz6j pv ehp horizontal disc. Th c 9z(3bmbie/ue disc rotates from rest with uniform angular acceleration α. After time t the objec9b bzi/m3 ce(ut slides off of the disc.
What is the linear speed of the object at this time?
A. $αt$
B. $rαt$
C. $\frac{1}{2}αt^2$
D. $\frac{1}{2}rαt^2$
