Directions: Read the passage and answer the questions that follow.
The strategic case for the Quadrilateral Security Dialogue, better known as the Quad, has always been sound. A rising China, with its authoritarian one-party system, is a challenge to the democratic order. It made sense, therefore, for democracies around China to pool their resources and strengths and present to the world a better and more sustainable model of governance. The strategic case for the Quad has, however, always faced a tactical hurdle. China was the factory of the world. It had become an almost indispensable cog in the global supply chain owing to its low-cost manufacturing prowess at a mass scale.
Select the word which is most SIMILAR in meaning to the word 'Indispensable' given in the passage?