Which of the following statements is valid?
(a) If the potential at a particular point is zero, the field at that point must be zero.
(b) If the field at a particular point is zero, the potential at that point must be zero.
(c) If the field throughout a particular region is constant, the potential throughout that region must be zero.
(d) If the potential throughout a particular region is constant, the field throughout that region must be zero.