帮忙做个题?谢谢!

what caused the accident and who was responsible for it ___a mysery. a.remains b.remain c.is d.look like
请帮忙选择,并说出原因.

帮忙做个题?谢谢! 帮忙 帮忙 帮忙 谢谢~~~ 谢谢帮忙~~~ 帮忙~谢谢 帮忙谢谢！！！ 谢谢帮忙！ 帮忙!~!谢谢 谢谢帮忙! 谢谢帮忙～～ 帮忙，谢谢