How can you get a best deal and save money when renting a car?
By ________ offered by different car rental companies.
comparing prices
（题目在问当你租车的时候， 你怎么能得到最好的交易和省钱。 根据原文“You also need to spend some time comparing prices offered by different car rental companies.” 可知， 需要花一些时间比较不同租车公司提供的价格。 所以空格处应填 comparing prices。）