The given options are all nouns, but only "โรงเรียน" (school) is a common noun that can refer to any school in general. The other options, "ขุขันธ์" (Khukhan), "ปรางค์กู่" (Prang Koo), and "ไพรบึง" (Phrai Bung), are all proper nouns that refer to specific places or names. Therefore, "โรงเรียน" is the correct answer as it is a common noun.