In a study of the forces involved when motor proteins move subcellular structures in cells, Shtridleman et al.* studied the motion of objects in living cells. In this paper, they extracted the position of a vesicle using video. Some of the frames are shown in the figure on the left below and a graph of the position of one of the vesicles that moved along a straight line (in a direction they call y) is shown on the right.

Six instants of time are identified on the graph and labeled by the letters A through F. Assuming that a smoothed model of the motion is appropriate for understanding the forces involved, choose the letter for the instant of time that would represent the events labeled in parts 1 through 4 below.1. The instant of time at which the vesicle is moving with the highest speed.

---Select--- A B C D E F