A Ball Is Connected by Two Massless Strings to a Horizontal

Multiple Choice

A ball is connected by two massless strings to a horizontal, rotating rod, and moves in a vertical circle. The strings are tied to the rod, are taut, and form two sides of an equilateral triangle. A photograph of the system is taken at moment t and is shown in the figure here. At t the centripetal acceleration of the ball is

A) horizontal and points right.
B) horizontal and points left.
C) zero.
D) vertical and points upward.
E) vertical and points downward.