很高兴为您
That these seas have been overfished has been known for years.
That these seas have been overfished 主语从句
these seas 主语
have been overfished 谓语,被动语态
该从句形式上没有宾语,但是其逻辑宾语其实就是主语的seas,不过在被动语态下变成了主语而已.
完整的句子核心是谓语,不及物动词没有宾语,祈使句没有主语.
has been 系动词 完成时态
known 表语
for years 时间状语
-------------------------------
★倾心解答★愿您满意★
★欢迎追问★敬请采纳★
-------------------------------