A characteristic which helps an animal to live longer will generally tend to become more common in the population because as the animal produces more offspring those traits are passed down to them. Eventually it will be a common characteristic in the population.
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Answer: c.They have a unique set of properties that can be used as identifiers.
Explanation:
Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.
Compounds can be decomposed into simpler constituents using chemical reactions.
Example: Water 
Compounds have different properties than the elements it is made up of.
Thus the most accurate description of compounds is that they have a unique set of properties that can be used as identifiers.
Just ignore such kind of people....
Answer:
Water is a polar solvent
Explanation:
We must know that pure dry hydrogen chloride gas does not show any acidic property.
In fact, when hydrogen chloride is dissolved in water, it breaks up into H3O^+ ions and Cl^- ions. This is possible because water is a polar solvent and assists the ionization of HCl.
In nonpolar solvents such as benzene, hydrogen chloride gas is not ionized hence it does not show any acidic property in a benzene solution.
