Answer: B: water
Step-by-step explanation:
Plucking is a phenomenon that is responsible for the erosion and transportation of individual pieces of rock under glaciers, specifically in "valley glaciers".
This phenomenon occurs at the base of the glacier as the ice drags along an uneven surface. The friction produced when the glacier moves down causes the ice to melt and that the water seeps into the cracks in the rocky surface below.
As the amount of ice increases, and therefore the friction increases, this action of freezing and thawing of the water generates more cracks in the soil, causing the rock to loosen and detach, being dragged by the flow of water. In this manner, these pieces of rock are incorporated into the ice that forms the glacial and become a part of it over time. Finally, the pieces of rock are transported by the glacial downhill until they are deposited.
In this way, the plucking phenomenon is caused by the solid and liquid water that makes up the glaciers, and since the ice is formed of water, the answer to your question is the option B.