Complete the following sentence with a (compound) word derived from the one(s) given in bracket.
It doesn't take much to improve the energy （ ） of your home. (efficient)
【正确答案】：EFFICIENCY
【题目解析】：
空格前为名词energy，后面是介词of，所以这里应该填一个名词构成名词短语、efficient的名词形式是efficiency。energy efficiency：能源效率。
句意：提高你家的能源效率并不需要花费太多。