A.
make 后跟 do,即动词原形；或跟形容词.如果用made,应该是：
this event made people sad./ this event made people be sad.（后一种语法上正确,但是基本不用）
cause 后面跟to do,即动词不定式；或跟名词.
this event caused people to be sad./this event caused sadness among people.
所以应选A.