Explanation:

Sugarcane requires a significant amount of water for its cultivation. It is considered one of the most water-intensive crops.

Sunflower, Pearl millet, and Red gram require comparatively less water for their growth and are more water-efficient.

In areas of water scarcity, cultivating water-intensive crops like sugarcane can put a strain on water resources.

Therefore, among the options given, Sugarcane is the least water-efficient crop.