The machine has been used many years. It’s no wonder that it doesn’t work well. A. regular

问题补充：

The machine has been used many years. It’s no wonder that it doesn’t work well.

A. regularly

B. constantly

C. occasionally

D. frequently

答案：

A. regularly

B. constantly

(答案→)C. occasionally

D. frequently

解析：A. regularly定期地，B. constantly 连续地，不断地，C. occasionally偶尔地，D. frequently经常地，句意：这个机器已经被使用了很多年，难怪它偶尔不工作了。所以选C。