the old man walked in the street ,为什么后接followed by his son ,

一个简单句只能有一个谓语动词.若非要用被动语态,可用and构成并列结构：
The old man walked in the street and he was followed by his son.
这种表达方式的意思侧重：老人在街上行走 和 老人的儿子跟在后面.
这种句式语法正确但不够简洁,所以将“he was followed by his son”变成一种表伴随状态的状语,就成了：The old man walked in the street followed by his son.
这种表达方式重点是：老人在街上行走.