การศึกษา, เส้นขยุกขยิก, สีน้ำตาล, แบบแผน, ดินสอ, ไม้บรรทัด, สามเหลี่ยม, การวัด, เรขาคณิต, วิทยาศาสตร์, อะตอม
Public Domain
ภาพถ่ายปลอดค่าลิขสิทธิ์ที่เกี่ยวข้อง
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