guinea pigs - Scientists will pay students to act as test subjects in their investigations into the causes of common colds. , organs - If your internal body parts don't work, you might die., immune systems - People's natural defences get weaker with age., mates - Male peacocks use their beautiful tails to attract female partners., offspring - The average dog can give birth to four or five puppies at one time., genes - The doctors think that the disease is caused by damage parts of DNA., paper - The was an academic article about animal communication in The Scientific Journal., proof - He didn't provide any evidence that his experiments had been successful. ,

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