C. Useful energy out of a system is always less than the energy input of that system.
Explanation:
The correct statement of the given options is that useful energy out of a system is always less than the energy input of that system.
This is in compliance with the third law of thermodynamics which states that "energy transformation in a system is not 100% efficient".
- At every stage energy is usually lost when it is transformed from one form to another.
- There is no machine that is 100% efficient.
- A machine that is 100% efficient will convert all the useful energy in it to do work and even more.
- In system energy is usually lost as a result of heat and to overcome friction.
- This reduces the amount of energy out of a system.
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Explanation:

Whether an added sugar contains more or less fructose versus glucose has little impact on health. (An exception may be people with diabetes who need to control their blood glucose, in which case a higher-fructose, lower-glucose sugar may be preferable
Answer:
This question is not well placed. It should be " a relationship between two organisms in which both benefit is called".
The answer is SYMBIOSIS
Explanation:
Living organisms tend to interact with one another in their natural environment. This interaction are of different types depending on the effect on the involved organisms. One of those interactions is SYMBIOSIS. Symbiosis is a relationship between two organisms in which both of the organisms benefit from one another.
An example is the relationship between the "CATTLE AND EGRET". The cattle provides food for the egret when they feed on the insect parasites on their body while the egret helps the cow get rid of detrimental parasites.