高三一道英语题,急

问题描述:

高三一道英语题,急
Where and how they found the boats with treasures ____ made knowm up to now.
A.hasn't been B.haven't beenC.wasn'tD.weren't
为什么选A?

up to now得出用现在完成时,”where and how they found the…treasures”整体作主语为三单,这整件事是被得知,所以还要用被动,综合起来为A