[单选题]
An object sits on a rotazv2xp qe2mg15- ( vqmkti dr*-e rqtz*k6ng horizontal disc. The disc rotates from rest with uniform angul6rkdq et-*r *zar acceleration α. After time t the object 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. $\frac{1}{2}rαt^2$
