Sarah decides to move to Hainan because she thinks that the air there is much fresher than

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A. one
B. those
C. ones
(答案→)D. that
解析：考查代词用法。One指代可数名词单数，表泛指；ones指代可数名词复数，表泛指；that指代不可数名词或者可数名词单数，后面必须有定语修饰，是特指；those指代可数名词复数，是特指。句意：Sarah决定搬去海南，因为她认为那里的空气要比这里的空气新鲜得多。