Japan was buried.

This question examines the main nutrients that the human body needs. Food contains six nutrients: protein, sugar, fat, vitamins, water and inorganic salts, each of which is essential for human body. Sugar is the most important energy-supplying substance for human body. The energy consumed by all human activities, including learning, walking, digestion and breathing, mainly comes from sugar, cereals, beans and roots. Trapped people can't eat or get sugar from food. The main purpose of delivering nutrient solution to the trapped people is to deliver glucose to them and provide energy for the human body. So choose B.