double letter

例句：

1. 1.The cost of the new product is doublethat of the old one.
   新产品的成本是旧产品的两倍。
2. 2. They doubled theirefforts to finish the project on time.
   他们加倍努力以按时完成项目。
3. 3. The companydoubled its profits last quarter.
   该公司上一季度的利润翻了一番。