A

When the pendulum starts to swing, the vessel experiences a change in orientation and acceleration due to the swinging motion.
Step 1: Consider the effects of inertia. As the pendulum swings to one side, the liquid inside the vessel will tend to stay at rest (due to inertia) and will rise higher on the opposite side of the vessel.
Step 2: The combined effect of the swing and the internal pressure redistributes the liquid's level, causing it to tilt.
Step 3: As the pendulum reaches its maximum displacement, the liquid will stabilize at a higher level on the side opposite to the direction of the swing.
Therefore, the conclusion is that the level of the liquid in the vessel will rise on the side opposite to the direction of the swing.