The correct answer is A. transpiration.
Transpiration is the process by which plants lose water vapor from their leaves. This is an important process for plants, as it helps to cool them down and to transport nutrients and minerals from the roots to the leaves. However, if a plant loses too much water, it will wilt.
Photosynthesis is the process by which plants use sunlight to convert carbon dioxide and water into glucose and oxygen. This is an essential process for plants, as it is how they produce food. However, photosynthesis does not cause plants to wilt.
Absorption is the process by which plants take in water and minerals from the soil. This is an important process for plants, as it is how they get the water and nutrients they need to survive. However, absorption does not cause plants to wilt.
Therefore, the correct answer is A. transpiration.