It is appropriate to have seven Dan in a rainy week.

There are many methods of artificial rainfall, which can shoot silver iodide shells above the zero-layer high-altitude clouds. You can also use dry ice. Dry ice is solid carbon dioxide, which is easy to sublimate. Dry ice absorbs heat during sublimation, which makes the temperature drop sharply. Water vapor in the air liquefies into small water droplets when it is cold, or directly condenses into small ice particles. Ice particles melt into raindrops in the process of falling and fall to the ground to form rain.

So choose C.