เบา, พื้นหลัง, มีสีเขียวขุ่น, รังสีของแสง, หลักสูตร, บทคัดย่อ, สีน้ำเงิน
Public Domain
ภาพถ่ายปลอดค่าลิขสิทธิ์ที่เกี่ยวข้อง
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