选must both
Both与动词连用时,大多数放在系动词be之后,其它动词之前.
如：His parents are both workers. They both enjoy reading.
若句中谓语动词包含情态动词或助动词时,both大多放在第一个情态动词或助动词之后.
如：The bridges must both be built this year.
两座桥都必须在今年修建.
kate and Mary have both gone to English.
凯特和玛丽都去了英国.