This question tests your understanding of synonyms. The word 'futile' means having no useful result; therefore, 'useless' is the closest synonym. 'Productive,' 'effective,' and 'successful' all imply a positive outcome, which is the opposite of 'futile'. **Core Concept:** Synonym identification **Solution Strategy:** Understand the meaning of 'futile' and find the option that has the closest meaning. **Option Analysis:** * A. Productive: Means creating or achieving a lot, the opposite of futile. * B. Effective: Means achieving a desired result, also the opposite of futile. * C. Useless: Means having no use or value, which is synonymous with futile. * D. Successful: Means achieving what is intended, again the opposite of futile. **Key Evidence:** The definition of futile directly points to the meaning of useless. **Common Mistake:** Confusing 'futile' with words that sound similar but have different meanings.