In order to explore the chemical properties of iron, Xiaoyu stuffed iron filings into a measuring cylinder with fluffy cotton and then buckled them upside down in water (pictured). A few days later, he observed. The measuring cylinder filled with iron filings is filled with fluffy cotton and then poured into water, so that iron will contact water and oxygen at the same time. After a few days, iron will rust and oxygen will be consumed, so the pressure in the measuring cylinder will become smaller. Under the action of atmospheric pressure, the liquid level in the measuring cylinder will rise. Observe the options, so choose: C.