The correct answer is "ขุนช้างขุนแผน". This is because "ขุนช้างขุนแผน" is a compound noun consisting of two words that describe a person or a title. "ขุนช้าง" refers to a noble or a high-ranking person, while "ขุนแผน" refers to a military strategist or a planner. Therefore, "ขุนช้างขุนแผน" is a proper noun that represents a specific person or a character. The other options, such as "โรงเรียน" (school), "ดอกไม้" (flowers), and "วรรณคดี" (literature), are not proper nouns or compound nouns that represent a specific person or title.