I find it interesting to sing.
She can hear nothing.
They were working.
He rushed into the office.
第一句原句中的it是宾语从句中的主语,同义句中做形式宾语的.
第二句否定后移.
第三句改为现在进行时,用动词的ing形式.
第四句went hurriedly与rush（冲）同义.