The lecture which lasted about three hours was so ____ that

The lecture which lasted about three hours was so ____ that the audience couldn’t help yawning.
A.clumsy B.bored C.tired D.tedious
请附带原因

本题应该选D
A.笨拙的,笨手笨脚的
B.无趣的 无聊的
C.疲劳的 累的
D.沉闷的,冗长乏味的
which lasted about three hours是一定语从句,修饰The lecture.本句话的主语是The lecture,如果选B,需要将bored 改为boring,因为bored修饰的人,boring修饰的是物.
这里你需要记住一点就可以了,修饰人时用ed,修饰物时用ing.
类似的词有：interested,interesting; frightened,frightening; tired,tiring;等等