A simple machine has efficiency 90%.What does it mean?No machine has 100%efficiency, Why?​

Of the four types of discharge, firing a. results from an employee's poor performance⎯that is, from his or her failure to fulfill expectations.b. is for-cause dismissal⎯the result of employee theft, gross insubordination, release of proprietary information, and so on.c. usually refers to the temporary unemployment experienced by hourly employees and implies that they are "subject to recall."d. designates the permanent elimination of a job as a result of workforce reduction, plant closing, or departmental consolidation.