If the ratio is 9:2 that means that 45 would by ñ times 9. At the same time, ñ must also fit the ratio. Using this knowledge, you can divide 45 by 9, giving you 5, then multiply it by 2. This means that the child is 10 years old.
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The answer is serotonin.
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C. Genetic variation
Bacteria are very numerous, and random mutation of bacterial DNA generates a wide variety of change, including resistance. It happens through mutation and selection. Not only are they capable of sharing genetic bits of DNA to related and unrealted species they can develop ways to remove the antibiotic before it reaches its intended area via biochemical pumps or enzymes to inactiavte the antibiotic.
The answer is B.- Upright bipedal walking posture.
