选C.
句意为：“父亲穿着邋遢、说话古怪的样子在现场的人看来一定像个傻老头.”
句子主干：Father must have appeared to be a silly old man.
appear to be...意思是“看起来、显得、似乎”
to the people present“对在场的人来说、在现场的人看来 ”
Dressed untidily and speaking in a strange way主语是father,即:
(Father was)Dressed untidily and （was）speaking in a strange way
在句中做非谓语成分,故省略.