Because of the beautiful water source, it is the dream of Nanchang people to build "China Water Capital". (1) People's understanding of the composition of water began with the experiment of hydrogen burning in oxygen. (1) Hydrogen burns to generate water, and the reaction equation is: 2H2+O2? Light it? . ? 2H2O

(2) Because white phosphorus easily reacts with oxygen in the air, when storing white phosphorus, it is put into water, and the function of water is to isolate the air;

(3) Because molecules are in motion, the "water cycle" on the earth's surface is mainly caused by the movement of water molecules;

(4) There are many ways to save water in life, such as washing the toilet with vegetable water and watering the flowers.

So, the answer is: (1)2H2+O2? Light it? . ? 2H2O(2)D； (3) water molecules; (4) Flush the toilet with vegetable washing water and water the flowers.