A charged ball B of finite mass is suspended in equilibrium by a string at an unknown angle with respect to the vertical, as shown below. The ball is surrounded by a horizontal external electric field (not shown in the figure). Which of the following statements could be true? (a) The ball is negatively charged, and the external electric field is directed leftward. (b) The ball is positively charged, and the external electric field is directed rightward. (c) Both (a) and (b) (d) Neither (a) nor (b)