Choose the alternative which can replace the bold word without changing the meaning of the sentence.  The success story of the factory is due to the indefatigable workers. 

In the sentence, "The success story of the factory is due to the indefatigable workers," the word "indefatigable" means that the workers are persistently tireless, showing an inability to be fatigued. Here are the options provided: 1.       tired - This is actually the opposite of indefatigable. 2.       skilful - While this is a positive attribute, it does not specifically relate to the aspect of tirelessness. 3.       brave - This describes courage, which is unrelated to the concept of tirelessness. 4.       tireless - This directly conveys the meaning of indefatigability, which is being untiring or ceaseless in effort. The word that best replaces "indefatigable" without changing the meaning of the sentence is: 4.       tireless