The correct option is C raisins placed in water swell.
Diffusion is the spreading of a substance from one point of concentration to a lesser concentrated point. Some examples of diffusion are such as a drop of food colouring in a cup of water, or a spritz of perfume filling the air, the spread of the tea infusion into the water from the bag.
When raisins are placed in water (a hypotonic solution), they absorb water by a process called osmosis and swell up.