Along a streamline
a) the velocity of a fluid particle remains constant
b) the velocity of all fluid particles crossing a given position is constant
c) the velocity of all fluid particles at a given instant is constant
d) the speed of a fluid particle remains constant
The answer is option (b) the velocity of all fluid particles crossing a given position is constant.
The speed at any point or any cross-section for a liquid is constant in the case of a streamlined flow.