The correct answer is:
A. Photosynthetic pigments absorb energy from light.

Ecosystems have trouble adjusting to short-term changes - This is false.
Eco system changes can be long term and short term. Few short-term environmental changes that can change an eco system are - drought, smog, volcanic eruptions, floods etc. An ecosystem can easily adapt to short-term changes. For example, after a forest fire plants can re-grow from their roots. Many species have features to help them cope with natural, short-term environmental changes.
Answer:
Water is a limited resource. It is needed for all living things and must be managed well to ensure we have enough for our needs and to protect our environment.