题目选项分析

Many utilities obtain most of their electric power from large coal and nuclear operations at costs that are sometimes two to three times higher than those for power from smaller, more efficient plants that can both make use of waste heat and take advantage of the current abundance of natural gas.

Many utilities obtain most of their electric power from large coal and nuclear operations at costs that are sometimes higher by two to three times as that from smaller, more efficient plants that both canmake use of waste heat and take advantage of the current abundance of natural gas.