[单选题]
An object is moving woz -4 7caqrexl8 d/wp(ith constant non-ze2zwi.cwqk mbd6 w*+w,ro velocity in the +x axis. The position versus.k,c+ 6wz2qwwwdm*bi time graph of this object is
A. a horizontal straight line.
B. a vertical straight line.
C. a straight line making an angle with the time axis.
D. a parabolic curve.