信誓旦旦

tā xìn shì dàn dàn de bǎo zhèng jué bù bǎ wǒ de mì mì shuō chū qu

她信誓旦旦地保证决不把我的秘密说出去。

She faithfully promised never to tell my secret.

tā xìn shì dàn dàn de shuō yī dìng yào bǎ cǐ shì gào dào fǎ tíng

她信誓旦旦地说一定要把此事告到法庭。

She vowed that she would take the matter to court.

tā men xìn shì dàn dàn de bǎo zhèng jiāng duì cǐ jué duì bǎo mì

他们信誓旦旦地保证将对此绝对保密。

They had given an absolute assurance that it would be kept secret.

xìn shì dàn dàn de xǔ nuò

信誓旦旦地许诺

make a serious promise