C is the correct answer because through the process of elimination, we know that European countries are trying to find energy sources the reduce the amount of air pollution, so A is not correct. Also, we know B is not correct because since fossil fuels aren't always widely available in Europe, drastically running out, and the population of the continent keeps increasing, European countries are struggling to keep up with the demand for fossil fuels. As a result, they are trying to find cheap, renewable energy resources to keep up with the demands of the ever-growing population. Let's skip to D. D is not correct at all because European countries actually <em>do </em>want to find new renewable energy sources, for the reasons stated in A and B. By investing in them, European countries are funding scientists to help harness the power of nature (solar, wind, hydroelectric, etc...). Let's go back to C. Yes, a huge amount of fossil fuels are used for fuel in a rocket, and scientists may be trying to find ways to use renewable energy instead of precious fossil fuels, but is that a main reason for European countries investing in new sources of energy? No, it may be a <em>minor </em>reason, not even a reason at all, but definitely <em>not </em>a main reason. After looking at answer choices A, B, and D, you can conclude C is not a reason for why European countries have invested in new sources of energy.
Hormones are molecules produced by glands which are transported by the circulatory system. Neurons, on the other hand, are cells that are designed to transmit information to other nerve cells, muscle or glands cells. They have a cell body, an axon, and dendrites. Neurons are the basic unit of the brain and their function is to transmit information.