National Learning Corporation. (2005). Sanitation worker: Test preparation study guide questions & answers. National Learning Corporation.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNational Learning Corporation. Sanitation Worker: Test Preparation Study Guide Questions & Answers. Syosset, N.Y.: National Learning Corporation, 2005.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNational Learning Corporation. Sanitation Worker: Test Preparation Study Guide Questions & Answers. National Learning Corporation, 2005.
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