[单选题]
If the position versus time graph of an object is a horizontal 2cm r6c-jk. gyline, the obj qrv4;wj;kjzc h6 6(gq8ub( woect is(j8wc;(qz6 k4 rjqu wo; b6ghv
A. moving with constant non-zero speed.
B. moving with constant non-zero acceleration.
C. at rest.
D. moving with infinite speed.
