Question

So far scientists have done a lot of research on Mars successfully.（改为被动语态）

So far a lot of research on Mars ________ ________ done successfully by scientists.

Answer

has been

【解析】

本句的受动着（宾语）是a lot of research on Mars，改为被动语态的主语；本句的谓语动词是“have done”现在完成时，改为被动语态为has/have been done，被动语态的主语a lot of research on Mars是第三人称单数，可知使用has；其他部分照抄，by+主动语态的主语（by scientists）放在句子的末尾。故答案为（1）has (2) been。