What can be done to add energy if a painting feels too cool and calm?

Correct answer: Add a small amount of warm colour

The governing concept is expressive colour temperature. Warm hues such as red, orange, and yellow are commonly associated with activity, liveliness, and visual emphasis. Adding a small warm accent can energise an overly cool composition without destroying its calm character. Increasing blue, green, or violet would generally reinforce coolness, while adding grey would mute the colours. Therefore, option A is correct.