The two adverbs nán dào (难道) and mò fēi (莫非) both could appear before verbs or subjects, mò fēi (莫非) is used more in literary language than nán dào (难道).
Rhetorical questions are not meant to elicit an answer but to make a point, nán dào (难道) could be used as a marker to form rhetorical questions and can produce an effect on emphasizing the mood of the rhetorical question, therefore, it is emphatic in tone. It should be noted that nán dào (难道) can only be used for rhetorical questions which could be answered with yes or no, this kind of rhetorical question sentence generally ends with the question marker ma (吗).
tā men kě yǐ zuò dào , nán dào wǒ men jiù zuò bù dào ma?
They can do it, can’t we do it?
(the speaker is sure that“we also can do it”)
tài yáng nán dào huì cóng xī biān shēng qǐ lái ma.
Will the sun rise from the west?
Nán dào (难道) and mò fēi (莫非) are interchangeable in most cases, but mò fēi (莫非) mainly expresses one’s doubt or conjecture to the situation, therefore, mò fēi (莫非) is less emphatic in tone than nán dào (难道).
tā xiàn zài hái méi qǐ chuáng ,nán dào tā bù zhī dào jīn tiān zǎo shàng yào kāi huì ma?
She hasn’t got up yet, doesn’t she know there is a meeting this morning?
tā xiàn zài hái méi qǐ chuáng, mò fēi tā bù zhī dào jīn tiān zǎo shàng yào kāi huì?
She hasn’t got up yet, could it be possible that she doesn’t know there is a meeting this morning?