four difficulty levels
四个难度等级
以上为机器翻译结果，长、整句建议使用 人工翻译 。
There are four difficulty levels like Simple, Medium, Difficult and Challenge.
有四个一样简单，中等，困难和挑战的难度级别。
youdao
And in my little world, there are four levels of economic difficulty.
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