Louis Pasteur conducted a famous experiment that addressed the question: "Can microorganisms generate spontaneously?" In his control group, he purified water in a closed flask by boiling it, and then let the water sit in the closed flask at room temperature for a predetermined period of time. In his experimental group, he purified water in an identical closed flask by boiling it. However, before letting the experimental water sit in its flask at room temperature for a predetermined period of time, he broke the top stem of the flask to expose the water to outside elements. After the predetermined period of time, Pasteur observed that there were no microorganisms in the control flask and that there were three thousand microorganisms in the experimental flask. Based on the results of this experiment, which of the following conclusions are valid?
\textrm{I}:I:start text, I, end text, colon When closed off to outside elements, purified water will not spontaneously generate microorganisms.
\textrm{II}:II:start text, I, I, end text, colon Exposing water to the elements causes the water to become harmful to humans.
\textrm{III}:III:start text, I, I, I, end text, colon Breaking the top stem of the experimental flask allowed the microorganisms to enter the purified water.
\textrm{IV}:IV:start text, I, V, end text, colon Not breaking the stem of the control flask prevented microorganisms from entering the purified water within.