The correct answer is option 3: sugarcane. Sugarcane is a major source of sugar because it contains high levels of sucrose, which is the main component of sugar. When sugarcane is processed, the juice extracted from the stalks undergoes various treatments to extract the sugar and remove impurities, resulting in the production of raw sugar. This raw sugar then undergoes further refining processes to produce refined white sugar, which is commonly used for cooking and sweetening food and beverages.

Option 1: Watermelon is not a major source of sugar compared to sugarcane. While watermelon does contain natural sugars like fructose, it is not high in sugar compared to other fruits.

Option 2: Beetroot also contains natural sugars like sucrose, but it is not a major source of sugar like sugarcane. Beetroot is often used for its nutritional properties and is not primarily grown for sugar production.

Option 4: Dates are naturally sweet and contain a significant amount of sugar, but they are not considered a major source of sugar compared to sugarcane. Dates are mainly consumed as a dried fruit and have various health benefits but are not used extensively for sugar production.

Therefore, the major source of sugar among the given options is option