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Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
Normal urine is sterile. It contains fluids, salts, and waste products. It is free of bacteria, viruses, and fungi.
The heart is located in the center of the chest, with part of it tipped slightly so that it taps against the left side of the chest.
Thyroid conditions cause a higher risk of fibromyalgia and chronic fatigue syndrome.
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