He has been working on this research these three years and (

答案：achieved
解析：
和前文重复的助动词或重复的主要动词也可省略（括号部分为省略的成分）.如：
1.you could have come and （you could have） told me.
2.please clean the classroom and （clean） the reading-room.
因为第二个【has】是前文重复的助动词,所以省略.