believed，were believed, were believing; sheep’ sheeps, sheeping What________to be aliens from outer space were actually several ________going astray.
【正确答案】：were believed; sheep
【题目解析】：此句的意思是被认为是外太空来的外星人其实是几只走丢的绵羊。该句是主语分句，分句what是主语后面需要跟谓语动词，被认为应用被动态。主句的谓语were后面是表语，走失的绵羊，在这里用了一个分词结构，绵羊作going的逻辑主语，分词的逻辑主语一般用所有格形式，如Do you mind my smoking?