บทคัดย่อ, สี, คำถาม, ใคร, อย่างไร, อะไร, ทำไม, ที่ไหน, เมื่อ, ปัญหา, สารละลาย
Public Domain
ภาพถ่ายปลอดค่าลิขสิทธิ์ที่เกี่ยวข้อง
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