A.I. Explanation:

Option 1: "Offering a range of health benefits"

Explanation: The text explicitly states that herbal teas offer a range of health benefits, including improved digestion, stress relief, and enhanced immune system function. This aligns directly with the main idea of the text, which emphasizes the medicinal properties of herbal teas.

Option 2: "Serving as a substitute for meals"

Explanation: This option is incorrect because the text does not mention herbal teas being used as meal substitutes. Instead, it focuses on their health benefits, making this statement irrelevant to the main idea.

Option 3: "Increasing caffeine consumption"

Explanation: This option is incorrect as herbal teas are typically caffeine-free, unlike traditional teas. The text does not support this statement, which contradicts the nature of herbal teas.

Option 4: "Enhancing the flavour of water"

Explanation: While herbal teas may enhance the flavour of water, this is not highlighted as a primary benefit in the text. The focus is on their health benefits, making this option too narrow and not aligned with the main theme.