难道:1 adv. used to reiterate a rhetorical question 河水难道会倒流吗?rivers never flow backward, don't they?
NOTE: the word 难道 can be echoed at the end of a sentence with the rhetorical word 不成 bu4 cheng2 难道他病了不成? He isn't ill, is he?
莫非:the same meaning as 难道, also can be echoed with the word 不成
indicating guessing or questioning
今天她又没来,莫非又生病了不成?She is absent today, can she be ill again?
万一:in case, eventually, if by any chance
以防万一
万一下雨也不要紧,我带伞了。
好歹:
1 good and bad, what's good and what's bad
这人真不知好歹。
2 mishap, disaster , risk
万一她有个好歹可怎么办?what if something should happen to her?
3 no matter in what way, anyhow , make do with sth 无论条件好坏,将就的做某事
时间太紧了,好歹多吃点就行了。the time is pressing, we'll order whatever there is.
4 in any case, anyhow, at any rate 不论如何
她要是在这里,好歹也能拿个主意。If she were here, she would give us some advice at any rate.