Pinyin
English Definition
whether or not
Phrase
wǒ méi bǎ wò shì fǒu suǒ le mén 。
I'm not sure whether I have locked the door.
tā kàn shàng qù xiàng shì nǐ de péng yǒu ， dàn wǒ huái yí tā shì fǒu shì zhēn xīn de 。
He appears to be your friend but I doubt if he is.