IELTS Academic Writing Task 1 Practice Test

The idea here is naming a landform. A large area of high, flat land is called a plateau. That term is the standard label for this feature, and using the indefinite article makes it a natural standalone noun phrase in everyday usage, which is why “A plateau” fits best. The other options describe related features but not the same one: a plain is low and flat, a mesa is a smaller, flat-topped hill with steep sides, and using just “plateau” without an article is less natural in a general noun-phrase answer.