Scientists divide vegetables into four categories: A, B, C and D according to the level of nutrients they contain. Category A vegetables: rich in carotene, riboflavin, vitamin C, calcium, fiber, etc., with high nutritional value, mainly including Chinese cabbage, spinach, mustard greens, amaranth, leeks, potherb, etc. Category B vegetables: The nutrients are inferior to those of Category A, and they are usually divided into three types. The first type contains riboflavin, including all fresh beans and bean sprouts; the second type contains more carotene and vitamin C, including carrots, celery, green onions, green garlic, tomatoes, peppers, sweet potatoes, etc.; the third type mainly contains vitamins C, including Chinese cabbage, cabbage, cauliflower, etc.

Category C vegetables: contain less vitamins but high in calories, including potatoes, yams, taro, pumpkin, etc. Ding vegetables: Contain a small amount of vitamin C and have low nutritional value, such as winter melon, bamboo shoots, eggplant, wild rice, etc.