问题：
Global hydroelectric power in theory is approximat
答案：
four times larger解析:本句中出现than表比较的词,并且所填空是在than之前,故此处应填比较的数字。本题涉及到全球水力发电与目前实际水力发电的利用的比较,故将答案出处定位到末段。该段首句提到Theoretical global hydroelectric power is approximately four times larger than the amount that has been taken advantage of today,其中题干中的in theory对应Theoretical,句型基本没有转换,故答案为。