simple kinematics

Q) Which of the following statements is/are false?

a) If two particles are neither approaching nor separating from each other, then their relative velocity is zero.

b) Four dogs are running along a line in same direction, such that each is running relative to the dog infront of him with equal speed. Then the rate of separation between the third and the first dog is same as that of the fourth and the second dog (where first, second, third and fourth are taken in order).

c) At some moment of time at a place, two projectiles are observed and it is found that their relative is zero. Then they will remain stationary w.r.t each other.

(Of (a) and (c) quite sure but unable to grasp (b))