Answer: B. Water breaks down into oxygen molecules for respiration.
Water is the required for photosynthesis, a process by which plants (terrestrial and aquatic) makes their food by utilizing water as a reactant to produce oxygen and glucose as product. The glucose act as a source of energy for conducting various metabolic processes in plants but oxygen is released in the air.

This oxygen is necessary for terrestrial and aquatic animals for respiration. Therefore, water breaks down into oxygen by the process of photosynthesis, hence water plays important role in respiration in living beings.
Answer: Ecology!
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The alkali metals in group l of the periodic table all have a single electron in the outermost shell. These metals form covalent bonds with for example the halogens, which have 7 electrons in their outer shell.
When the alkali metal halide, such as KCl is dissolved in water, it dissociates into ions. The K atom loses the single electron, and therefore has a positive charge. In turn, the chloride atom gains the electron and becomes the negatively charged chloride ion.
Answer: Stars?
Explanation: I think it is stars because there is only one star in our solar system. I don't know for sure if it is, but I think it is. Don't be too sure of my answer.