The forest problem is in many ways the most vital internal problem of the United States. The more closely this statement is examined the more evident its truth becomes. In the arid regions of the West agricultural prosperity depends first of all upon the available water supply. Forest protection alone can maintain the streamflow necessary for irrigation in the West and prevent floods destructive to agriculture and manufactures in the East. The relation between forests and the whole mineral industry is an extremely intimate one, for mines cannot be developed without timber, and usually not without timber close at hand.
Which sentence BEST describes the central idea of the passage?
Forests are in trouble from too little water.
Forests are indispensable to key parts of the economy.
Trees prevent streams in forests from flooding farming areas.
Timber from forests provides critical support for the mining industry.