请教下，这个到底是做什么成份呢？？由prep1-33想到的

prep1-33

More than 300 rivers drain into Siberia's Lake Baikal, which holds 20 percent of the world's fresh water, more than all the North American Great Lakes combined.

划线部分到底是做什么成分呢？注释说是做20 percent of the world's fresh water的同位语，可是我查了下同位语的用法，没有类似这种结构的啊

prep1-44

Scientists at the Los Alamos National Laboratory have  succeeded for the first time in mining heat from Earth's interior to produce energy on a commercial scale, enough for generating electricity efficiently and for heating factories and homes.

个人感觉，这题的划线部分和上题的很类似，难道这里的是energy的同位语吗？

prep1-33 more than all the North American Great Lakes combined 是 前面figure的同位语。从逻辑意思也可以判断出来。Siberia's Lake Baikal 拥有20%的全球淡水，这个数字比北美五大湖合起来还多。

prep1-44 不是同位语 enough...是想修饰前面的scale.