instruction:
Given a scientific passage and an answer, generate a question for the given answer.
question:
Passage: All compounds form when atoms of different elements share or transfer electrons. In water, the atoms share electrons. In some other compounds, called ionic compounds , atoms transfer electrons. The electrons actually move from one atom to another. When atoms transfer electrons in this way, they become charged particles called ions. The ions are held together by ionic bonds. Answer: ions
answer:
When electrons move from one atom to another, they become what?

question:
Passage: Figure 43.17 Rising and falling hormone levels result in progression of the ovarian and menstrual cycles. (credit: modification of work by Mikael Haggstrom). Answer: hormones
answer:
Rising and falling levels of what will result in progression of the ovarian and menstrual cycles?

question:
Passage: Much of the time, you probably aren't aware of your digestive system. It works well without causing any problems. But most people have problems with their digestive system at least once in a while. Did you ever eat something that didn't "agree" with you? Maybe you had a stomachache or felt sick to your stomach. Perhaps you had diarrhea. These can be symptoms of food poisoning. Answer: digestive system
answer:
Diarrhea due to food poisoning is an example of a problem involving what organ system?