When a spherical ball is dropped into a viscous liquid, it initially accelerates due to gravity . According to the sources, as the ball's speed ($v$) increases, the retarding viscous force acting against its motion also increases (Stokes' Law: $F = 6\pi\eta a v$) . Consequently, the net downward acceleration decreases over time . Eventually, the sum of the upward viscous force and the buoyant force exactly equals the downward force of gravity . At this equilibrium point, the net force becomes zero, and the ball continues to move at a constant speed known as the terminal velocity ($v_t$) . The velocity-time graph for this motion starts at the origin (zero speed), increases at a decreasing rate, and asymptotically approaches a horizontal line representing the terminal velocity. Graph B (referenced as BBB) correctly depicts this relationship.