The simple subject is the noun or pronoun in the sentence that stands alone. In the sentence given, the clause,<em> </em><em>billions of tax dollars, stands as the subject of the sentence. The simple subject is the 'dollars' that was described by the other preceding descriptors. </em>
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The predicate is, spent on dollar exploration. The simple predicate is spent. The predicate is the verb that stands alone in the sentence and describes the action.
