From what I can tell, The answer is either A or B. Mammals have what is called an Endoskeleton, which means that their skeletons are inside their bodies. A way to remember this is Exo- is similar to exit and when you exit something then you are going outside. Endo- sounds like into, which can relate to being on the inside. Insects have Exoskeletons, which are made from Chitin. Now Agonists are also called Prime Mover muscles, which means they are practically the same thing.
Bacteria that change nitrogen gas from the atmosphere into solid nitrogen usable by plants are called nitrogen-fixing bacteria. These bacteria are found both in the soil and in symbiotic relationships with plants.
I'd use the library, the encyclopedia and the Internet.
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Cats also purr when they are nervous or in pain, leading some experts to believe that this uniquely feline vocalization is actually a method of self-healing. A domestic cat's purr has a frequency of between 25 and 150 Hertz, which happens to be the frequency at which muscles and bones best grow and repair themselves.
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