[单选题]
If the position versus time graph of an object i 9nha o( t1agz/0fj/hvs a vertical line, the jjci mcg*49niy-j3-2fl fw:e object is4 fmji3w-fjy* g: 9jl2cne ci-
A. moving with constant non-zero speed.
B. moving with constant non-zero acceleration.
C. at rest.
D. moving with infinite speed.
