In the game, a Pony Express rider controlled by the game player has to avoid obstacles and pick up letters in search of the e（） 100 percent rating.（－－difficult to find, define, or achieve）

In the game, a Pony Express rider controlled by the game player has to avoid obstacles and pick up letters in search of the e（） 100 percent rating.（--difficult to find, define, or achieve）
正确答案：elusive