Because: Some of the work done by the machine is used to overcome the friction created by the use of the machine. ... Work output can never be greater than work input. Machines allow force to be applied over a greater distance, which means that less force will be needed for the same amount of work.
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Viruses enter a host cell when the host cell recognizes and binds the glycoproteins on the virus's surface, then take in the virus by phagocytosis. Thus, d. is the correct answer.
I think the correct answer is nucleic acid. There four major classes of macromolecules and these are lipids, carbohydrates, proteins and nucleic acids. Among these nucleic acid would best fit the definition. Examples of nucleic acids are DNA and RNA.