Making an excavator may be not rocket science, but for a man with only a middle school education, it is truly impressive. A 25-year-old man spent three months to design and three days to make an excavator in Sichuan province. He spent less than 40,000 yuan making it when a commercially available model costs 100,000 yuan or even 200,000 yuan.

How many years did the man spent on designing the excavator?

A. three years

B. three months

C. three days

（中國日報網英語點津 江巍 編輯）