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In an experiment a controlled variable is one that can be changed but is not for the duration of the experiment. For example, temperature in the room during a chemical reaction can be set at a specific limit like 42 degrees. That variable is constant. The temperature change inside the actual reaction vessel cannot be … Read more
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Women who have a problem getting pregnant due to a lack of healthy sperm from the man, or uterine problems that don't allow an egg to attach to the wall of the uterus thus become impregnated, or ovarian cysts (fairly common) might not release an egg or the fallopian tubes may be obstructed and will … Read more